Journal of applied physiology
-
Comparative Study
Comparison between the effect of static contraction and tendon stretch on the discharge of group III and IV muscle afferents.
The exercise pressor reflex is evoked by both mechanical and metabolic stimuli. Tendon stretch does not increase muscle metabolism and therefore is used to investigate the mechanical component of the exercise pressor reflex. An important assumption underlying the use of tendon stretch to study the mechanical component of the exercise pressor reflex is that stretch stimulates the same group III mechanosensitive muscle afferents as does static contraction. ⋯ On average, the conduction velocities of the 18 group III afferents that responded to static contraction (11.6 +/- 1.6 m/s) were significantly slower (P = 0.03) than those of the 14 group III afferents that responded to tendon stretch (16.7 +/- 1.5 m/s). We have concluded that tendon stretch stimulated a different population of group III mechanosensitive muscle afferents than did static contraction. Although there is some overlap between the two populations of group III mechanosensitive afferents, it is not large, comprising less than half of the group III afferents responding to static contraction.
-
Twenty-one subjects with asthma underwent treadmill exercise to exhaustion at a workload that elicited approximately 90% of each subject's maximal O2 uptake (EX1). After EX1, 12 subjects experienced significant exercise-induced bronchospasm [(EIB+), %decrease in forced expiratory volume in 1.0 s = -24.0 +/- 11.5%; pulmonary resistance at rest vs. postexercise = 3.2 +/- 1.5 vs. 8.1 +/- 4.5 cmH2O.l(-1).s(-1)] and nine did not (EIB-). The alveolar-to-arterial Po2 difference (A-aDo2) was widened from rest (9.1 +/- 6.7 Torr) to 23.1 +/- 10.4 and 18.1 +/- 9.1 Torr at 35 min after EX1 in subjects with and without EIB, respectively (P < 0.05). ⋯ During the second exercise bout, pulmonary resistance decreased to baseline levels in the EIB+ group and the A-aDo2 and PaO2 returned to match the values seen during EX1 in both groups. Sputum histamine (34.6 +/- 25.9 vs. 61.2 +/- 42.0 ng/ml, pre- vs. postexercise) and urinary 9alpha,11beta-prostaglandin F2 (74.5 +/- 38.6 vs. 164.6 +/- 84.2 ng/mmol creatinine, pre- vs. postexercise) were increased after exercise only in the EIB+ group (P < 0.05), and postexercise sputum histamine was significantly correlated with the exercise PaO2 and A-aDo2 in the EIB+ subjects. Thus exercise causes gas-exchange impairment during the postexercise period in asthmatic subjects independent of decreases in forced expiratory flow rates after the exercise; however, a subsequent exercise bout normalizes this impairment secondary in part to a fast acting, robust exercise-induced bronchodilatory response.
-
We studied mechanical ventilatory constraints in 13 aerobically trained (Tr) and 11 untrained (UT) prepubescent children by plotting the exercise flow-volume (F-V) loops within the maximal F-V loop (MFVL) measured at rest. The MFVL allowed to determine forced vital capacity (FVC) and maximal expiratory flows. Expiratory and inspiratory reserve volumes relative to FVC (ERV/FVC and IRV/FVC, respectively) were measured during a progressive exercise test until exhaustion. ⋯ However, higher ventilation (V(E)), ERV/FVC, and dyspnea associated with lower BR, IRV/FVC, and SaO2 were reported at peak power in Tr than UT (P < 0.05). These results suggest that, because of their higher Ve level, trained children presented higher ventilatory constraints than untrained. These may influence negatively the SaO2 level and dyspnea during strenuous exercise.
-
Comparative Study
Respiratory control stability and upper airway collapsibility in men and women with obstructive sleep apnea.
Obstructive sleep apnea (OSA) is two to three times more common in men as in women. The mechanisms leading to this difference are currently unclear but could include gender differences in respiratory stability [loop gain (LG)] or upper airway collapsibility [pharyngeal critical closing pressure (Pcrit)]. The aim of this study was to compare LG and Pcrit between men and women with OSA to determine whether the factors contributing to apnea are similar between genders. ⋯ In the BMI-matched subgroup, women had less severe OSA during non-rapid eye movement sleep (30.9 +/- 7.4 vs. 52.5 +/- 8.1 events/h; P = 0.04) and lower Pcrit (-2.01 +/- 0.62 vs. 1.16 +/- 0.83 cmH2O; P = 0.005). However, LG was not significantly different between genders (0.38 +/- 0.02 vs. 0.33 +/- 0.03; P = 0.14). These results suggest that women may be protected from developing OSA by having a less collapsible upper airway for any given degree of obesity.
-
Comparative Study
Effectiveness of mask and helmet interfaces to deliver noninvasive ventilation in a human model of resistive breathing.
The helmet, a transparent latex-free polyvinyl chloride cylinder linked by a metallic ring to a soft collar that seals the helmet around the neck, has been recently proposed as an effective alternative to conventional face mask to deliver pressure support ventilation (PSV) during noninvasive ventilation in patients with acute respiratory failure. We tested the hypothesis that mechanical characteristics of the helmet (large internal volume and high compliance) might impair patient-ventilator interactions compared with standard face mask. Breathing pattern, CO(2) clearance, indexes of inspiratory muscle effort and patient-ventilator asynchrony, and dyspnea were measured at different levels of PSV delivered by face mask and helmet in six healthy volunteers before (load-off) and after (load-on) application of a linear resistor. ⋯ Autocycled breaths accounted for 12 and 25% of the total minute ventilation and for 10 and 23% of the total inspiratory muscle effort during mask and helmet PSV, respectively. We conclude that PSV delivered by helmet interface is less effective in unloading inspiratory muscles compared with PSV delivered by standard face mask. Other ventilatory assist modes should be tested to exploit to the most the potential benefits offered by the helmet.