Altered thermoregulatory responses after 15 days of head-down tilt

1994 ◽  
Vol 77 (4) ◽  
pp. 1863-1867 ◽  
Author(s):  
C. G. Crandall ◽  
J. M. Johnson ◽  
V. A. Convertino ◽  
P. B. Raven ◽  
K. A. Engelke
Keyword(s):  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Forearm Blood Flow ◽  
Whole Body ◽  
Adult Males ◽  
Thermally Induced ◽  
Thermoregulatory Responses ◽  
Forearm Vascular Conductance ◽  
Extended Exposure

To determine whether extended exposure to a simulation of microgravity alters thermoregulatory reflex control of skin blood flow, six adult males (mean age 40 +/- 2 yr) were exposed to 15 days of 6 degrees head-down tilt (HDT). On an ambulatory control day before HDT exposure and on HDT day 15, the core temperature of each subject was increased by 0.5–1.0 degree C by whole body heating with a water-perfused suit. Mean skin temperature, oral temperature (Tor), mean arterial pressure, and forearm blood flow were measured throughout the protocol. Forearm vascular conductance (FVC) was calculated from the ratio of forearm blood flow to mean arterial pressure. After HDT exposure, the Tor threshold at which reflex thermally induced increases in FVC began was elevated (36.87 +/- 0.06 to 37.00 +/- 0.09 degrees C; P = 0.043), whereas the slope of the Tor-FVC relationship after this threshold was reduced (13.7 +/- 2.3 to 9.5 +/- 1.1 FVC units/degrees C; P = 0.038). Moreover, normothermic FVC and FVC at the highest common Tor between pre- and post-HDT trials were reduced after HDT (normothermic: 4.2 +/- 0.5 to 3.0 +/- 0.4 ml.100 ml-1.min-1.100 mmHg-1, P = 0.04; hyperthermic: 12.4 +/- 1.0 to 7.8 +/- 0.7 ml.100 ml-1.min-1.100 mmHg-1, P < 0.001). These data suggest that HDT exposure reduces thermoregulatory responses to heat stress. The mechanisms resulting in such an impaired thermoregulatory response are unknown but are likely related to the relative dehydration that accompanies this exposure.

Hypohydration affects forearm vascular conductance independent of heart rate during exercise

1992 ◽  
Vol 73 (4) ◽  
pp. 1232-1237 ◽  
Author(s):  
C. G. Tankersley ◽  
D. H. Zappe ◽  
T. G. Meister ◽  
W. L. Kenney
Keyword(s):  
Heart Rate ◽  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Forearm Blood Flow ◽  
Body Core Temperature ◽  
Esophageal Temperature ◽  
Vascular Conductance ◽  
Cutaneous Vasodilation ◽  
Forearm Vascular Conductance ◽  
Body Core

Elevated body core temperature stimulates cutaneous vasodilation, which can be modified by nonthermal factors. To test whether hypohydration affects forearm vascular conductance discretely from relative alterations in heart rate (HR), eight trained cyclists exercised progressively for 20 min each at 60, 120, and 180 W [approximately 22, 37, and 55% of maximal cycling O2 consumption (VO2peak), respectively] in a warm humid environment (dry bulb temperature 30 degrees C; wet bulb temperature 24 degrees C). Esophageal temperature and forearm blood flow were measured every 30 s, and mean arterial pressure and HR were measured at rest and during each exercise intensity (minutes 15, 35, and 55). In the hypovolemic (HP) compared with the euvolemic (EU) state, blood volume was contracted by 24-h fluid restriction an average of 510 ml, and this difference was sustained throughout exercise. The esophageal temperature and HR responses were similar between EU and HP states at 60 and 120 W but were significantly (P < 0.05) higher in HP by the end of 180 W. In contrast, the forearm blood flow response was significantly (P < 0.05) depressed during exercise at 120 and 180 W in HP, whereas mean arterial pressure remained similar between conditions. When body core temperature is elevated in a hypohydrated state, forearm vascular conductance is reduced at exercise intensities of approximately 37% VO2peak, which is independent of relative changes in HR. These findings are consistent with the notion that during exercise an attenuated cutaneous vasodilation is elicited by alterations in regionalized sympathetic outflow, which is unaccompanied by activation of cardiac pacemaker cells.

scholarly journals Aerobic training and cutaneous vasodilation in young and older men

1999 ◽  
Vol 86 (5) ◽  
pp. 1676-1686 ◽  
Author(s):  
Carla M. Thomas ◽  
Jane M. Pierzga ◽  
W. Larry Kenney
Keyword(s):  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Aerobic Training ◽  
Older Men ◽  
Vascular Conductance ◽  
Doppler Flowmetry ◽  
Forearm Vascular Conductance ◽  
Response To Exercise ◽  
Cutaneous Vascular Conductance

To determine the effect and underlying mechanisms of exercise training and the influence of age on the skin blood flow (SkBF) response to exercise in a hot environment, 22 young (Y; 18–30 yr) and 21 older (O; 61–78 yr) men were assigned to 16 wk of aerobic (A; YA, n = 8; OA, n = 11), resistance (R; YR, n = 7; OR, n = 3), or no training (C; YC, n = 7; OC, n = 7). Before and after treatment, subjects exercised at 60% of maximum oxygen consumption (V˙o 2 max) on a cycle ergometer for 60 min at 36°C. Cutaneous vascular conductance, defined as SkBF divided by mean arterial pressure, was monitored at control (vasoconstriction intact) and bretylium-treated (vasoconstriction blocked) sites on the forearm using laser-Doppler flowmetry. Forearm vascular conductance was calculated as forearm blood flow (venous occlusion plethysmography) divided by mean arterial pressure. Esophageal and skin temperatures were recorded. Only aerobic training (functionally defined a priori as a 5% or greater increase inV˙o 2 max) produced a decrease in the mean body temperature threshold for increasing forearm vascular conductance (36.89 ± 0.08 to 36.63 ± 0.08°C, P < 0.003) and cutaneous vascular conductance (36.91 ± 0.08 to 36.65 ± 0.08°C, P < 0.004). Similar thresholds between control and bretylium-treated sites indicated that the decrease was mediated through the active vasodilator system. This shift was more pronounced in the older men who presented greater training-induced increases in V˙o 2 maxthan did the young men (22 and 9%, respectively). In summary, older men improved their SkBF response to exercise-heat stress through the effect of aerobic training on the cutaneous vasodilator system.

Passive triceps surae stretch inhibits vasoconstriction in the nonexercised limb during posthandgrip muscle ischemia

2004 ◽  
Vol 97 (5) ◽  
pp. 1681-1685 ◽  
Author(s):  
Ken Tokizawa ◽  
Masaki Mizuno ◽  
Yoshio Nakamura ◽  
Isao Muraoka
Keyword(s):  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Forearm Blood Flow ◽  
Triceps Surae ◽  
Muscle Ischemia ◽  
Forearm Vascular Conductance ◽  
Muscle Mechanoreceptor ◽  
Baseline Values ◽  
Exercise Muscle ◽  
The Right

We investigated whether selective muscle mechanoreceptor activation in the lower limb opposes arm muscle metaboreceptor activation-mediated limb vasoconstriction. Seven subjects completed two trials: one control trial and one stretch trial. Both trials included 2 min of handgrip and 2 min of posthandgrip exercise muscle ischemia (PEMI). In the stretch trial, a 2-min sustained triceps surae stretch, by brief passive dorsiflexion of the right foot, was performed simultaneously during PEMI. Mean arterial pressure, heart rate, and forearm blood flow (FBF) in the nonexercised arm and forearm vascular conductance (FVC) in the nonexercised arm were measured. During PEMI in the control trial, mean arterial pressure was significantly greater and FBF and FVC were significantly lower than baseline values ( P < 0.05 for each). In contrast, FBF and FVC during PEMI in the stretch trial exhibited different responses than in the control trial. FBF and FVC were significantly greater in the stretch trial than in the control trial (FBF, 5.5 ± 0.4 vs. 3.8 ± 0.4 ml·100 ml−1·min−1; FVC, 0.048 ± 0.004 vs. 0.033 ± 0.003 unit, respectively; P < 0.05). These results indicate that passive triceps surae stretch can inhibit vasoconstriction in the nonexercised forearm mediated via muscle metaboreceptor activation in the exercised arm.

Is nitric oxide involved in cutaneous vasodilation during body heating in humans?

1994 ◽  
Vol 76 (5) ◽  
pp. 2047-2053 ◽  
Author(s):  
N. M. Dietz ◽  
J. M. Rivera ◽  
D. O. Warner ◽  
M. J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Heart Rate ◽  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Forearm Blood Flow ◽  
No Synthase ◽  
Oral Temperature ◽  
Drug Infusion ◽  
Cutaneous Vasodilation

The neurotransmitter responsible for neurogenic vasodilation in human skin during body heating is unknown. We sought to determine whether the vasodilating substance nitric oxide (NO) is involved in this phenomenon. Six subjects were heated for 50 min by use of a water-perfused suit while forearm blood flow (FBF) was measured with plethysmography and skin blood flow (SkBF) was measured by the laser-Doppler method in both arms. In one forearm, NG-monomethyl-L-arginine (L-NMMA), an NO synthase blocker, was infused into the brachial artery. Bolus doses of L-NMMA (< or = 4 mg/min) for 5 min were given to blunt NO-mediated vasodilator responses to acetylcholine (ACh, 64 micrograms/min). A continuous infusion of L-NMMA (< or = 1.0 mg/min) was used during body heating to maintain NO synthase blockade. In the forearm receiving L-NMMA, FBF was 1.8 +/- 0.3 ml.100 ml-1.min-1 before drug infusion and rose to 9.5 +/- 1.3 ml.100 ml-1.min-1 with ACh. After L-NMMA infusion, FBF was 1.3 +/- 0.2 ml.100 ml-1.min-1 and rose to 2.6 +/- 0.4 ml.100 ml-1.min-1 with ACh (both P < 0.05 vs. pre-L-NMMA). Similar changes in SkBF were seen with ACh and L-NMMA, confirming that the drugs reached cutaneous vessels. With body heating, oral temperature increased by 1.2 degrees C, heart rate increased by 34 beats/min, and mean arterial pressure remained constant at approximately 75 mmHg. FBF in the treated forearm rose to 11.5 +/- 2.1 vs. 12.6 +/- 1.7 ml.100 ml-1.min-1 in the control forearm (P > 0.05, control vs. treated response).(ABSTRACT TRUNCATED AT 250 WORDS)

Atropine-induced cutaneous vasodilation decreases esophageal temperature during exercise

1989 ◽  
Vol 257 (5) ◽  
pp. R1089-R1095 ◽  
Author(s):  
M. A. Kolka ◽  
L. A. Stephenson ◽  
A. E. Allan ◽  
P. B. Rock
Keyword(s):  
Heart Rate ◽  
Blood Flow ◽  
Forearm Blood Flow ◽  
Sensible Heat Flux ◽  
Whole Body ◽  
Adult Males ◽  
Local Skin ◽  
Cutaneous Vasodilation ◽  
Human Use ◽  
Skin Temperatures

Four healthy adult males volunteered for this study, which followed informed-consent procedures administered by our local Human Use Committee. Esophageal (Tes) and mean skin (Tsk, eight site) temperatures, forearm sweating rate (ms), metabolism (M), heart rate (HR), and forearm blood flow (FBF) were measured at rest and during forearm blood flow (FBF) were measured at rest and during exercise [55% oxygen consumption (Vo2) peak] during control experiments and after 2 mg im atropine (ATR). Experiments were randomized and separated by at least 72 h. ATR increased heart rate at rest by 15 beats/min and during exercise by 24 beats/min. ATR decreased whole body sweating by 57%. All eight local skin temperatures were higher in ATR than in control. Tsk was 32.6 degrees C in ATR and 31.0 degrees C in control (P less than 0.01). During exercise, ATR increased vasodilation of the forearm compared with control. The slope of FBF to Tes increased over 300% in ATR experiments compared with control (P less than 0.05). The higher sensible heat flux from this vasodilation decreased Tes during exercise, which further decreased sweating. Skin blood flow remained elevated as Tes decreased, suggesting that local vasodilatory factors promoted atropine-induced cutaneous vasodilation.

Reflex peripheral vasoconstriction is diminished in older men

1996 ◽  
Vol 80 (2) ◽  
pp. 512-515 ◽  
Author(s):  
W. L. Kenney ◽  
C. G. Armstrong
Keyword(s):  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Oxygen Uptake ◽  
Arterial Pressure ◽  
Maximal Oxygen Uptake ◽  
Age Groups ◽  
Older Men ◽  
Whole Body ◽  
Peripheral Blood Flow ◽  
Age Difference

The purpose of this study was to compare reflex control of limb blood flow in healthy young (Y; 26 +/- 2 yr) and older (O;61 +/- 2 yr) men during whole body cooling under resting conditions. To better isolate the effect of chronological age, the two age groups (n = 6 per group) were closely matched for maximal oxygen uptake, body surface area, skinfold thickness, and fat-free weight. Subjects sat in an environmentally controlled chamber clad in standardized (0.6-clo) light cotton clothing at a dry-bulb temperature (Tdb) of 28 degrees C. After 30 min, Tdb was decreased by 2 degrees C every 5 min until Tdb = 10 degrees C, where it was held constant for the remainder of the 120-min session. Esophageal and mean skin temperatures were monitored continuously. Forearm blood flow (FBF) was measured every 5 min by venous occlusion plethysmography by using a mercury-in-Silastic strain gauge while arm temperature between the wrist and elbow was clamped at 37.2 +/- 0.1 degrees C by localized warm air heating. In this way, limb vasoconstriction was driven solely by thermoregulatory reflexes and not by direct effects of localized cooling. Mean skin temperature decreased at a similar rate and to a similar extent (by approximately 6 degrees C over a 2-h period) in both age groups, whereas esophageal temperature was relatively unaffected. In response to the local heating, the Y group maintained a significantly higher FBF than did the O group during the initial 30 min but decreased FBF during the cooling phase at a greater rate and to a greater extent than did the O group, leading to a significantly lower FBF during the final 30 min (at Tdb = 10 degrees C). Because there was no age difference in the mean arterial pressure response, similar effects of age were seen on forearm vascular conductance (FBF/mean arterial pressure). It was concluded that older men have a diminished reflex limb vasoconstrictor response to skin cooling. Furthermore, this difference in control of peripheral blood flow appears to be related to age per se; i.e., it is not a reflection of age-related differences in maximal oxygen uptake or body composition.

scholarly journals Ten days of repeated local forearm heating does not affect cutaneous vascular function

2017 ◽  
Vol 123 (2) ◽  
pp. 310-316 ◽  
Author(s):  
Michael A. Francisco ◽  
Vienna E. Brunt ◽  
Krista Nicole Jensen ◽  
Santiago Lorenzo ◽  
Christopher T. Minson
Keyword(s):  
Blood Flow ◽  
Young Adults ◽  
Mean Arterial Pressure ◽  
Arterial Pressure ◽  
Vascular Function ◽  
Forearm Blood Flow ◽  
Local Heating ◽  
Laser Doppler ◽  
Vascular Conductance ◽  
Doppler Flowmetry

The aim of the present study was to determine whether 10 days of repeated local heating could induce peripheral adaptations in the cutaneous vasculature and to investigate potential mechanisms of adaptation. We also assessed maximal forearm blood flow to determine whether repeated local heating affects maximal dilator capacity. Before and after 10 days of heat training consisting of 1-h exposures of the forearm to 42°C water or 32°C water (control) in the contralateral arm (randomized and counterbalanced), we assessed hyperemia to rapid local heating of the skin ( n = 14 recreationally active young subjects). In addition, sequential doses of acetylcholine (ACh, 1 and 10 mM) were infused in a subset of subjects ( n = 7) via microdialysis to study potential nonthermal microvascular adaptations following 10 days of repeated forearm heat training. Skin blood flow was assessed using laser-Doppler flowmetry, and cutaneous vascular conductance (CVC) was calculated as laser-Doppler red blood cell flux divided by mean arterial pressure. Maximal cutaneous vasodilation was achieved by heating the arm in a water-spray device for 45 min and assessed using venous occlusion plethysmography. Forearm vascular conductance (FVC) was calculated as forearm blood flow divided by mean arterial pressure. Repeated forearm heating did not increase plateau percent maximal CVC (CVCmax) responses to local heating (89 ± 3 vs. 89 ± 2% CVCmax, P = 0.19), 1 mM ACh (43 ± 9 vs. 53 ± 7% CVCmax, P = 0.76), or 10 mM ACh (61 ± 9 vs. 85 ± 7% CVCmax, P = 0.37, by 2-way repeated-measures ANOVA). There was a main effect of time at 10 mM ACh ( P = 0.03). Maximal FVC remained unchanged (0.12 ± 0.02 vs. 0.14 ± 0.02 FVC, P = 0.30). No differences were observed in the control arm. Ten days of repeated forearm heating in recreationally active young adults did not improve the microvascular responsiveness to ACh or local heating. NEW & NOTEWORTHY We show for the first time that 10 days of repeated forearm heating is not sufficient to improve cutaneous vascular responsiveness in recreationally active young adults. In addition, this is the first study to investigate cutaneous cholinergic sensitivity and forearm blood flow following repeated local heat exposure. Our data add to the limited studies regarding repeated local heating of the cutaneous vasculature.

Effect of mild essential hypertension on control of forearm blood flow during exercise in the heat

1984 ◽  
Vol 56 (4) ◽  
pp. 930-935 ◽  
Author(s):  
W. L. Kenney ◽  
E. Kamon ◽  
E. R. Buskirk
Keyword(s):  
Blood Flow ◽  
Arterial Pressure ◽  
Core Temperature ◽  
Forearm Blood Flow ◽  
Impedance Plethysmography ◽  
Maximal Aerobic Capacity ◽  
Significant Linear Correlation ◽  
Actual Range ◽  
Leg Exercise ◽  
Cutaneous Blood

Six essential hypertensive (resting mean arterial pressure, MAP greater than 110 mmHg) and eight normotensive (resting MAP less than 95 mmHg) men, aged 30–58 yr, were tested during 1 h of dynamic leg exercise in the heat. Environmental conditions were fixed at 38 degrees C dry-bulb temperature and 28 degrees C wet-bulb temperature; exercise intensity was preset to approximate 40% of each subject's maximal aerobic capacity (actual range 38–43%). Forearm blood flow (FBF) was measured by impedance plethysmography. The intergroup difference in arterial pressure was maintained but not increased or decreased during exercise in the heat. FBF increased in both groups, but the increase was significantly less for the hypertensive subjects. FBF showed a significant linear correlation (different from 0) with core temperature in seven of eight control subjects but in none of the hypertensive subjects. The magnitude of FBF increase was inversely proportional to resting MAP (r = -0.89). It was concluded that essential hypertensive subjects respond to exercise in the heat with a diminished FBF response related to an alteration in control relative to central (core temperature) influences. This may be due to an imbalance between thermal and nonthermal (baroreflex) mechanisms controlling cutaneous blood flow.

Abstract 032: Uninterrupted Sitting Induces Unfavorable Changes In Resting Hemodynamics And Inflammatory And Vascular Biomarkers In Physically Inactive And Active Adults

Circulation ◽  
2021 ◽  
Vol 143 (Suppl_1) ◽  
Author(s):  
Megan C Nelson ◽  
Madeline P Casanova ◽  
Jennavere R Ball ◽  
Rachel D Midence ◽  
Timothy R Johnson ◽  
...  
Keyword(s):  
Physical Activity ◽  
Blood Flow ◽  
Mean Arterial Pressure ◽  
Shear Rate ◽  
Arterial Pressure ◽  
Vascular Function ◽  
Blood Velocity ◽  
Inflammatory Biomarkers ◽  
Active Adults ◽  
Over Time

Introduction: A single bout of uninterrupted sitting impairs vascular function in the legs, which may be due to reductions in blood flow and shear stress. Participating in regular moderate-to-vigorous physical activity (MVPA) has been identified as an effective approach for improving vascular function, and recent evidence suggests meeting the physical activity (PA) guidelines may attenuate some of the negative health outcomes associated with excessive sedentary behavior; however, it is not well understood how meeting the PA guidelines may influence the acute response to sitting. Our aim was to investigate the effects of 3 h of uninterrupted sitting on hemodynamics and vascular and inflammatory biomarkers in physically inactive and active adults. Hypothesis: We hypothesized active adults would experience less detrimental physiological changes after sitting compared to inactive adults. Methods: Eleven inactive (mean±SD, age: 47.1±8.9 y, body fat: 33.1±8.5%; 78.5% women) and 16 active adults (age: 46.1±8.9 y, body fat: 25.2±7.2%; 31.1% women) completed 3 h of uninterrupted sitting. Adults self-reported their PA with the International PA Questionnaire. Adults engaging in ≥150 min·wk -1 were classified as active and <150 min·wk -1 , inactive. Hemodynamic variables, and superficial femoral artery (SFA) diameter and blood velocity were measured each hour over 3 h of sitting. Mean arterial pressure, blood flow and shear rate were calculated. Serum vascular and inflammatory biomarkers were measured pre and post sitting. Linear mixed-effects modeling was used to assess changes in dependent variables over time and between inactive and active adults, controlling for sex. Results: Inactive and active adults self-reported 7.3±7.1 and 93.3±64.8 min·d -1 of MVPA, respectively. Endothelin-1 (baseline: 8.3±13.4 pg/mL, post: 81.1±103.0 pg/mL; p<0.001) and interleukin-6 (baseline: 0.08±0.06 pg/mL, post: 0.11±0.11 pg/mL; p=0.03) increased post sitting compared to baseline in all adults, regardless of PA status. Systolic blood pressure, mean arterial pressure, calf circumference, and SFA diameter, blood velocity, and mean blood flow decreased over time in both groups (p<0.05 for all). There was an interaction effect for mean shear rate (p=0.008); inactive adults experienced a decline over 3 h of sitting (baseline: 76.1±48.2 s -1 ; 1 h: 55.0±27.4 s -1 ; 2 h: 45.3±24.2 s -1 ; 3 h: 40.8±25.5 s -1 ) while active participants demonstrated no change (baseline: 36.6±21.4 s -1 ; 1 h: 28.1±21.4 s -1 ; 2 h: 26.1±20.9 s -1 ; 3 h: 23.8±19.5 s -1 ). Inactive adults also had a higher oscillatory shear index compared to active adults (p<0.001). Conclusion: Uninterrupted sitting induced unfavorable changes regardless of PA status; however, active adults demonstrated a more favorable shear profile. Meeting PA guidelines may attenuate some unfavorable changes within the vasculature associated with prolonged sitting.

Sign in / Sign up

Export Citation Format

Share Document