Effect of capillary pressure and lung distension on capillary recruitment

To investigate the effect of capillary pressure and alveolar distension on capillary recruitment, we used video-microscopy to quantify capillary recruitment in individual subpleural alveolar walls. Canine lobes were perfused with autologous blood either while inflated by positive airway pressure or while inflated by negative intrapleural pressure in the intact thorax with airway pressure remaining atmospheric. Low flow rates minimized the arteriovenous pressure gradient (< 5 mmHg), permitting capillary pressure estimation by averaging these pressures. Capillary pressure was varied stepwise from airway pressure to 30 mmHg above airway pressure. Capillary recruitment always began as capillary pressure exceeded airway pressure. At low positive airway pressures, the capillaries of the excised lobes opened suddenly over a narrow pressure range. AT higher airway pressures and in the intact thorax, recruitment occurred over a wide range of capillary pressures. We conclude that capillary perfusion begins when intracapillary pressure just exceeds alveolar pressure but that further increases in capillary pressure recruit capillaries depending on tension in the alveolar wall, whether imposed by positive airway pressure or by gravity when the lung is suspended in an intact thorax.

Download Full-text

A Randomized Trial of Low-Flow Oxygen versus Nasal Continuous Positive Airway Pressure in Preterm Infants

Neonatology ◽

10.1159/000437203 ◽

2015 ◽

Vol 108 (4) ◽

pp. 259-265 ◽

Cited By ~ 3

Author(s):

Christian Heiring ◽

Jesper Steensberg ◽

Mia Bjerager ◽

Gorm Greisen

Keyword(s):

Continuous Positive Airway Pressure ◽

Randomized Trial ◽

Preterm Infants ◽

Airway Pressure ◽

Positive Airway Pressure ◽

Low Flow

Download Full-text

PEEP and CPAP

Anaesthesia and Intensive Care ◽

10.1177/0310057x8601400304 ◽

1986 ◽

Vol 14 (3) ◽

pp. 236-250 ◽

Cited By ~ 49

Author(s):

A. W. Duncan ◽

T. E. Oh ◽

D. R. Hillman

Keyword(s):

Airway Pressure ◽

Positive Airway Pressure ◽

Work Of Breathing ◽

Lung Compliance ◽

Raised Intracranial Pressure ◽

Positive End Expiratory Pressure ◽

Pulmonary Barotrauma ◽

Endotracheal Tubes ◽

Wide Range ◽

Residual Capacity

Positive end-expiratory pressure (PEEP) maintains airway pressure above atmospheric at the end of expiration, and may be used with mechanical ventilation or spontaneous breathing. CPAP, or continuous positive airway pressure, refers to spontaneous ventilation with a positive airway pressure being maintained throughout the whole respiratory cycle. PEEP/CPAP primarily improves oxygenation by increasing functional residual capacity, and may increase lung compliance and decrease the work of breathing. PEEP/CPAP may be applied using endotracheal tubes, nasal masks or prongs, or face masks or chambers to treat a wide range of adult and paediatric respiratory disorders. Complications associated with their use relate to the pressures applied and include pulmonary barotrauma, decreased cardiac output and raised intracranial pressure.

Download Full-text

Influence of acute pulmonary vascular congestion on recoiling force of excised cats' lung

Journal of Applied Physiology ◽

10.1152/jappl.1959.14.6.905 ◽

1959 ◽

Vol 14 (6) ◽

pp. 905-908 ◽

Cited By ~ 25

Author(s):

N. R. Frank

Keyword(s):

Airway Pressure ◽

Left Atrial ◽

Technical Assistance ◽

Narrow Range ◽

Elastic Behavior ◽

Tidal Breathing ◽

Lung Volumes ◽

Airway Pressures ◽

Vascular Congestion ◽

Wide Range

The effects of acute reversible pulmonary vascular congestion on the elastic behavior of excised cats' lungs were studied in 10 preparations. Measurements were made of changes in airway pressure at constantly held lung volumes over a wide range of deflation. To achieve vascular congestion left atrial pressure was raised to 20 and 30 cm H2O. Two effects were noted; one was that the slope of the volume-pressure relations of the lungs was slightly reduced at all levels of deflation, the other, the effect of vascular congestion on the recoiling force of the lungs was a function of the volume of the lungs at which congestion was induced. At large volumes (airway pressures of 5 cm H2O or more) recoiling force was increased; at intermediate volumes (airway pressures of 2.5 and 3 cm H2O) the change was negligible and, at smaller volumes, it was reduced in a manner consistent with the early work of von Basch. The findings suggest that there is a volume of the lungs, or perhaps a narrow range of volume, at which the lungs and blood vessels exert least mechanical stress on each other. This volume is believed to lie close to that in which tidal breathing occurs. Note: (With the Technical Assistance of Elcanor Gotz) Submitted on April 17, 1959

Download Full-text

Low flow continuous positive airway pressure with a modified fresh gas reservoir

Critical Care Medicine ◽

10.1097/00003246-198102000-00009 ◽

1981 ◽

Vol 9 (2) ◽

pp. 106-108 ◽

Cited By ~ 9

Author(s):

MITCHELL E. ZEBROWSKI ◽

RALPH T. GEER

Keyword(s):

Continuous Positive Airway Pressure ◽

Airway Pressure ◽

Positive Airway Pressure ◽

Low Flow ◽

Gas Reservoir

Download Full-text

The use of low flow nasal prongs therapy versus self ventilation in weaning neonates from nasal continuous positive airway pressure (NCPAP). The NOFLO trial

Archives of Disease in Childhood ◽

10.1136/archdischild-2012-301885.320 ◽

2012 ◽

Vol 97 (Suppl 1) ◽

pp. A134.1-A134

Author(s):

S O'Donnell ◽

S Curry ◽

N Buggy ◽

M Moynihan ◽

S Sebkova ◽

...

Keyword(s):

Continuous Positive Airway Pressure ◽

Airway Pressure ◽

Positive Airway Pressure ◽

Low Flow

Download Full-text

Increased microvascular permeability in dog lungs due to high peak airway pressures

Journal of Applied Physiology ◽

10.1152/jappl.1984.57.6.1809 ◽

1984 ◽

Vol 57 (6) ◽

pp. 1809-1816 ◽

Cited By ~ 169

Author(s):

J. C. Parker ◽

M. I. Townsley ◽

B. Rippe ◽

A. E. Taylor ◽

J. Thigpen

Keyword(s):

Capillary Pressure ◽

Safety Factor ◽

Airway Pressure ◽

Plasma Proteins ◽

Microvascular Permeability ◽

Edema Formation ◽

Osmotic Effect ◽

Airway Pressures ◽

Tissue Safety ◽

Total Tissue

The effect of peak airway pressure (Paw) on vascular permeability and the "safety factor" against edema formation was determined in isolated blood-perfused lower lobes of dog lungs. Microvascular permeability was evaluated using the measured filtration coefficient (Kf,C), isogravimetric capillary pressure (Pc,i), and critical capillary pressure (Pcrit) for exhaustion of tissue safety factors. Airway pressure was maintained constant at -3 cmH2O except for the test period of 20 min when the lungs were ventilated at 6/min with sufficient volume to generate a peak inflation pressure ranging from 5 to 60 cmH2O. Mean Kf,C (in ml X min-1 X cmH2O X 100 g-1) were measured before and immediately after the period of peak airway pressures. Kf,C was significantly increased in all lungs where Paw exceeded 42 cmH2O, but in only two experiments at a lower Paw. Mean Pc,i was significantly reduced from control in the 45-55 and 55-65 cmH2O Paw groups, and both Pc,i and Pcrit were found to be inversely related to Kf,C measured after Paw ventilation. These data indicate that ventilation with Paw above 42 cmH2O (30.9 Torr) and in some cases lower pressures for 20 min significantly increased capillary hydraulic conductivity, reduced the effective osmotic effect of plasma proteins at the capillary wall, and reduced the total tissue safety factor against edema formation.

Download Full-text

The Use of Bubble CPAP and Humidified High Flow Nasal Cannula Oxygen Therapy in Children with Severe Pneumonia and Hypoxemia: A Systematic Review of the Evidence

Bangladesh Critical Care Journal ◽

10.3329/bccj.v2i2.24085 ◽

2015 ◽

Vol 2 (2) ◽

pp. 71-78

Author(s):

Mohammod Jobayer Chisti ◽

Trevor Duke ◽

Tahmeed Ahmed ◽

KM Shahunja ◽

Abu SMSB Shahid ◽

...

Keyword(s):

Respiratory Distress ◽

Airway Pressure ◽

Oxygen Therapy ◽

Positive Airway Pressure ◽

Severe Pneumonia ◽

High Flow ◽

Low Flow ◽

Older Children ◽

High Flow Nasal Cannula ◽

Bubble Cpap

Background: Among children with severe pneumonia hypoxemia is the commonest complication leading to death. Some children will have both type I (hypoxemic) and type II (hypercarbic) respiratory failure. Together this accounts for high case-fatality rates in most populations with severe pneumonia. Standard oxygen supplementation by nasal prongs (low flow) can be lifesaving, but is not always sufficient to manage respiratory failure. In recent years continuous positive airway pressure (CPAP) has been used to relieve hypoxemia and reduce the work of breathing. There are several ways to give positive airway pressure; one is bubble CPAP (BCPAP), another is high flow nasal cannula (HFNC) oxygen therapy.Objective: To review the evidence for using BCPAP, and HFNC therapy in children with severe pneumonia and hypoxemia, particularly the experience of these therapies in developing countries.Methods: Two of our study investigators independently conducted searches of the existing literature in PUBMED in October 2014 to identify reports focusing on the use of BCPAP or HFNC therapy in children with severe pneumonia and hypoxemia, as defined by the World Health Organization.Results: 13 relevant studies were identified. Ten evaluated the efficacy of BCPAP among 3164 children, and three described the same for HFNC in 255 children. In all studies the entry criteria was severe respiratory distress. The study methodologies, the outcomes recorded and results were heterogeneous. The age range of the children in the studies was from the immediate newborn period on day 1 of life up to the age of 12 years. However, we evaluated the outcome of our review in two aged categories and found: children 0-28 days for 8 studies and > 28 days for 2 studies. In 3 studies of children aged 0-28 days and 2 studies of older children had clinical features consistent with severe pneumonia and those who among them were treated with immediate BCPAP therapy had better outcome (p<0.01 or CI < 1) compared to those who were treated with delayed BCPAP, or historical control one each, or standard flow flow (LF) oxygen therapy (in two studies). Primary outcomes were comparable between BCPAP and ventilator driven CPAP in three studies and between BCPAP and low flow oxygen or variable flow nasal CPAP in two studies (95% CI contain 1) of children aged 0-28 days. Children treated with HFNC compared to those who did not receive HFNC in three relevant studies, all of them in older children had better outcome (p<0.05).Conclusion: Studies of BCPAP and HFNC are heterogeneous with different populations, comparators, outcome measures and results. However limited studies suggest that BCPAP may be effective in managing respiratory distress and hypoxemia in developing countries, although evidence is not overwhelming. Studies of the use of HFNC therapy are more limited and do not allow firm conclusions to be made. Most studies of BCPAP and HFNC have been done in neonates with respiratory distress, and studies outside this age group, where the predominant pathologies are bacterial pneumonia, sepsis and viral bronchiolitis are needed.Bangladesh Crit Care J September 2014; 2 (2): 71-78

Download Full-text

Distribution of red and white blood cells in alveolar walls

Journal of Applied Physiology ◽

10.1152/jappl.1975.38.1.117 ◽

1975 ◽

Vol 38 (1) ◽

pp. 117-124 ◽

Cited By ~ 8

Author(s):

S. Perlo ◽

A. A. Jalowayski ◽

C. M. Durand ◽

J. B. West

Keyword(s):

Pulmonary Artery ◽

Capillary Pressure ◽

Blood Cells ◽

Mononuclear Cells ◽

Human Lung ◽

White Blood Cells ◽

Alveolar Wall ◽

Point Counting ◽

Alveolar Pressure ◽

Capillary Recruitment

Dog lungs were perfused with blood and rapidly frozen with liquid Freon gas at various pulmonary artery and venous pressures. The numbers of red and white blood cells per mm-2 of alveolar wall were counted in lung sections and, in addition, the proportion (by area) of the wall occupied by the cells was measured by point counting. The number and proportional area of the red blood cells rapidly increased as perfusing pressure was raised. These findings are consistent with earlier observations of capillary recruitment and distension. An unexpected observation was the large number of leukocytes in the capillaries especially at low perfusing pressures. For example when arterial exceeded alveolar pressure by 5 cmH2O (as occurs near the apex of the upright human lung), there were about 5,000 red cells and 4,000 white cells per mm-2 of alveolar wall. As perfusing pressure was increased, the number of leukocytes paradoxically decreased in zone 3 but remained constant in zone 2. Most of the white cells were mononuclear cells. These results suggest that the lung behaves as a mechanical sieve for large cells and that the number of trapped cells depends on the capillary pressure.

Download Full-text