Changes in Diaphragmatic Function Induced by an Increased Inspiratory Load Experienced by Military Divers: An Ultrasound Study

Background: Inspiratory loading is experienced by military divers when they use rebreather device. Our objective was to assess the changes in diaphragm function induced by an increase in inspiratory load at values similar to those experienced by divers in real life.Methods: We recorded the excursion and the thickness of the right hemidiaphragm in 22 healthy male volunteers under inspiratory load conditions, using ultrasound in B- and M-mode. The measurements were performed at tidal volume and during breathing at 50% of inspiratory capacity. The breathing rate was regulated and similar in the various sessions with and without load.Results: The rebreather device used by French military divers leads to an increase in inspiratory load of close to 30 cmH2O. Consequently, the session under load was performed using a device set to this threshold. Significant increases in the excursion and the thickening fraction of the diaphragm were observed between the sessions at tidal volume and at high volume. With addition of the inspiratory load, the excursion of the right hemidiaphragm increased significantly from 2.3 to 3.4cm at tidal volume and from 3.9 to 4.7cm at high volume. The thickening fraction increased significantly from 30.4 to 76.6% at tidal volume and from 70 to 123% at high volume. The statistical analysis demonstrated that assessment of the changes of the thickening fraction during breathing at tidal volume was the most relevant marker to assess the impact of the inspiratory load on the diaphragm.Conclusion: Diaphragm ultrasound can be used to assess the changes in the diaphragm contraction pattern secondary to an increase in the respiratory load that can be generated by use a diving apparatus. The recording of the changes of the motion, and more importantly of the thickness of the diaphragm, during the breathing cycle is able to provide relevant information regarding the inspiratory load.

Sleep deprivation reduces vagal tone during an inspiratory endurance task in humans

Study Objectives Sleep deprivation alters inspiratory endurance by reducing inspiratory motor output. Vagal tone is involved in exercise endurance. This study aimed to investigate the effect of sleep deprivation on vagal tone adaptation in healthy subjects performing an inspiratory effort. Methods Vagal tone was assessed using Heart Rate Variability normalized units of frequency domain component HF (high frequency) before, at the start, and the end of an inspiratory loading trial performed until exhaustion by 16 volunteers after one night of sleep deprivation and one night of normal sleep, where sleep deprivation reduced the inspiratory endurance by half compared to the normal sleep condition (30min vs 60 min). Results At rest, heart rate was similar in sleep deprivation and normal sleep conditions. In normal sleep condition, heart rate increased during inspiratory loading task; this increase was greater in sleep deprivation condition. In normal sleep condition, vagal tone increased at the beginning of the trial. This vagal tone increase was absent in sleep deprivation condition. Conclusions Sleep deprivation abolished vagal tone response to inspiratory load, possibly contributing to a higher heart rate during the trial and to a reduced inspiratory endurance.

Inspiratory loading exercises on respiratory muscle function in post-operative gastroplasty patients: a randomized clinical trial

Introduction: The gastroplasty post-operative period can alter respiratory mechanics and predispose patients to respiratory complications. Objective: The objective was to evaluate the effects of exercises with inspiratory load on respiratory muscle function and on the prevalence of atelectasis after gastroplasty. Method: 40 participants were randomly allocated into two groups: Control Group (CG), its members underwent conventional respiratory physical therapy (CRP) and the Inspiratory Load Group (ILG), its members performed exercises with linear inspiratory pressure load, with 40% of the maximum inspiratory pressure (MIP), associated with CRP. Therapy procedures were conducted twice during the immediate post-operative period and thrice on the first post-operative day. In addition to evaluating the MIP, the nasal inspiratory pressure (NIP) and the sustained maximum inspiratory pressure (SMIP) were evaluated before and after treatment. Analysis of variance followed by the Bonferroni correction were applied considering a 5% significance level (p < 0.05). Results: There was no significant difference in NIP and SMIP values when the pre- and post-operative periods were compared for the ILG; however, these values were significantly lower for the CG, also with intergroup differences in NIP values. Atelectasis prevalence was 5% for ILG and 15% for CG, with no intergroup difference. Conclusion: The inspiratory muscle strength and resistance of the respiratory muscles were maintained in the group that performed exercises with inspiratory load associated with CRP, with a low rate of atelectasis after gastroplasty.

AIRWAY POSITIVE PRESSURE VS. EXERCISES WITH INSPIRATORY LOADING FOCUSED ON PULMONARY AND RESPIRATORY MUSCULAR FUNCTIONS IN THE POSTOPERATIVE PERIOD OF BARIATRIC SURGERY

ABSTRACT Background: Bariatric surgery can trigger postoperative pulmonary complications due to factors inherent to the procedure, mainly due to diaphragmatic dysfunction. Aim: To evaluate and compare the effects of two levels of positive pressure and exercises with inspiratory load on lung function, inspiratory muscle strength and respiratory muscle resistance, and the prevalence of atelectasis after gastroplasty. Methods: Clinical, randomized and blind trial, with subjects submitted to bariatric surgery, allocated to two groups: positive pressure group, who received positive pressure at two levels during one hour and conventional respiratory physiotherapy and inspiratory load group, who performed exercises with load linear inspiratory pressure, six sets of 15 repetitions, in addition to conventional respiratory physiotherapy, both of which were applied twice in the immediate postoperative period and three times a day on the first postoperative day. Spirometry was performed for pulmonary function analysis, nasal inspiratory pressure for inspiratory muscle strength and incremental test of respiratory muscle resistance for sustained maximal inspiratory pressure, both preoperatively and on hospital discharge on the second postoperative day. Results: There was no significant difference (p> 0.05) in the expiratory reserve volume and in the tidal volume in the pre and postoperative periods when compared intra and intergroup. There was no significant difference (p>0.05) in the nasal inspiratory pressure and the maximal inspiratory pressure maintained in the inspiratory load group in the intragroup evaluation, but with a significant difference (p<0.05) compared to the positive pressure group. The prevalence of atelectasis was 5% in both groups with no significant difference (p>0.05) between them. Conclusion: Both groups, associated with conventional respiratory physiotherapy, preserved expiratory reserve volume and tidal volume and had a low atelectasis rate. The inspiratory loading group still maintained inspiratory muscle strength and resistance of respiratory muscles.

Experimental dyspnea as a stressor: differential cardiovegetative responses to inspiratory threshold loading in healthy men and women

Dyspnea is associated with an emotional reaction that involves limbic activation. The inspiratory threshold load (ITL) is known to elicit a dyspneic response in healthy subjects. Laboratory-induced stress conditions have been shown to elicit sex-related differences in cardiovascular responses. The aim of this study was to evaluate how healthy men ( n = 8) and women ( n = 9) react and adapt to 5-min periods of ITL at three levels (low, medium, and high) in terms of heart rate (HR), temporal (RMSSD) and spectral (LF, HF, LF/HF ratio) HRV indexes, and rating of breathing discomfort. HR increased with low, medium, and high ITL in men, whereas it increased only with high ITL in women. LF/HF ratio increased at low ITL in both men and women. Modifications appear to depend essentially on increased LF in men and on reduced HF in women. In addition, HRV modifications differ between men and women, following the order of presentation of ITLs. Our results show a continuous and sustained stress in men (increased HR, LF, and LF/HF ratio across ITL presentation) and a stress adaptation in women. Subjective responses of breathing discomfort were not correlated with sympatho-vagal balance modifications for a subgroup of subjects ( n = 10). Breathing against the ITL induced autonomic modifications that are different between men and women, i.e., driven by sympathetic mediated responses in men, whereas women showed a greater parasympathetic modulation of cardiovascular activity. These results highlight the role of the mechanical inspiratory load in the heart rate variability seen in chronic obstructive pulmonary disease. NEW & NOTEWORTHY Breathing against the ITL induced autonomic modifications driven by sympathetic mediated responses in men, whereas women showed a greater parasympathetic modulation of cardiovascular activity, even for low load. A stress circuit could be at the origin of autonomic modifications induced by ITL. Our results would underline the role of the mechanic inspiratory load in the abnormalities in heart rate variability seen in COPD patients.