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At least 739 records · Page 41Linked to original sources
PubMed1996

Effects of N2O narcosis on breathing and effort sensations during exercise and inspiratory resistive loading.

The influence of nitrous oxide (N2O) narcosis on the response to exercise and inspiratory resistive loading was studied in thirteen male US Navy divers. Each diver performed an incremental bicycle exercise test at 1 ATA to volitional exhaustion while breathing a 23% N2O gas mixture and a nonnarcotic gas of the same PO2, density and viscosity. The same gas mixtures were used during four subsequent 30-min steady-state submaximal exercise trials in which the subjects breathed the mixtures both with and without an inspiratory resistance (5.5 vs. 1.1 cmH2O.s.l-1 at 1 l/s). Throughout each test, subjective ratings of respiratory effort (RE), leg exertion, and narcosis were obtained with a category-ration scale. The level of narcosis was rated between slight and moderate for the N2O mixture but showed great individual variation. Perceived leg exertion and the time to exhaustion were not significantly different with the two breathing mixtures. Heart rate was unaffected by the gas mixture and inspiratory resistance at rest and during steady-state exercise but was significantly lower with the N2O mixture during incremental exercise (P < 0.05). Despite significant increases in inspiratory occlusion pressure (13%; P < 0.05), esophageal pressure (12%; P < 0.001), expired minute ventilation (4%; P < 0.01), and the work rate of N2O mixture, RE during both steady-state and incremental exercise was 25% lower with the narcotic gas than with the nonnarcotic mixture (P < 0.05). We conclude that the narcotic-mediated changes in ventilation, heart rate, and RE induced by 23% N2o are not sufficient magnitude to influence exercise tolerance at surface pressure. Furthermore, the load-compensating respiratory reflexes responsible for maintaining ventilation during resistive breathing are not depressed by N2O narcosis.

Adult↗
PubMed2005

The influence of the self-contained breathing apparatus (SCBA) on ventilatory function and maximal exercise.

Our previous work showed that breathing low density gases during exercise with the self-contained breathing apparatus (SCBA) improves maximal ventilation (V(E)) and maximal oxygen consumption (VO(2)max). This suggests that the SCBA limits exercise by adding a resistive load to breathing. In this study we compared VO(2)max with and without the various components comprising the SCBA to determine their impact on VO(2)max. Twelve males performed 4 randomly ordered incremental exercise tests to exhaustion on a treadmill: (1) low-resistance breathing valve only (CON); (2) full SCBA (SCBA); (3) SCBA regulator only (REG); and (4) carrying the cylinder and harness assembly but breathing through a low-resistance breathing valve (PACK). Compared to CON, VO(2)max was reduced to a similar extent in the SCBA and REG trials (14.9% and 13.1%, respectively). The PACK condition also reduced VO(2)max, but to a lesser extent (4.8 +/- 5.3%). At VO(2)max, VE was decreased and expiratory mouth pressure and external breathing resistance (BR) were increased in both the SCBA and REG trials. There was a significant correlation between the change in maximal V(E)and VO(2)max with the SCBA. The results show that the SCBA reduces VO(2)max by limiting V(E) secondary to the increased BR of the SCBA regulator.

Adult↗
PubMed1992

13CO2 washout dynamics during intermittent exercise in children and adults.

To test the hypothesis that children store less CO2 than adults during exercise, we measured breath 13CO2 washout dynamics after oral bolus of [13C]bicarbonate in nine children [8 +/- 1 (SD) yr, 4 boys] and nine (28 +/- 6 yr, 5 males) adults. Gas exchange [O2 uptake and CO2 production (Vco2)] was measured breath by breath during rest and during light (80% of the anaerobic threshold) intermittent exercise. Breath samples were obtained for subsequent analysis of 13CO2 by isotope ratio mass spectrometry. The tracer estimate of Vco2 was highly correlated to Vco2 measured by gas exchange (r = 0.97, P < 0.0001). The mean residence time was shorter in children (50 +/- 5 min) compared with adults (69 +/- 7 min, P < 0.0001) at rest and during exercise (children, 35 +/- 7 min; adults, 50 +/- 11 min, P < 0.001). The estimate of stored CO2 (using mean Vco2 measured by gas exchange and mean residence time derived from tracer washout) was not statistically different at rest between children (254 +/- 36 ml/kg) and adults (232 +/- 37 ml/kg). During exercise, CO2 stores in the adults (304 +/- 46 ml/kg) were significantly increased over rest (P < 0.001), but there was no increase in children (mean exercise value, 254 +/- 38 ml/kg). These data support the hypothesis that CO2 distribution in response to exercise changes during the growth period.

Adult↗
PubMed2002

Pulmonary gas exchange and acid-base state at 5,260 m in high-altitude Bolivians and acclimatized lowlanders.

Pulmonary gas exchange and acid-base state were compared in nine Danish lowlanders (L) acclimatized to 5,260 m for 9 wk and seven native Bolivian residents (N) of La Paz (altitude 3,600-4,100 m) brought acutely to this altitude. We evaluated normalcy of arterial pH and assessed pulmonary gas exchange and acid-base balance at rest and during peak exercise when breathing room air and 55% O2. Despite 9 wk at 5,260 m and considerable renal bicarbonate excretion (arterial plasma HCO3- concentration = 15.1 meq/l), resting arterial pH in L was 7.48 +/- 0.007 (significantly greater than 7.40). On the other hand, arterial pH in N was only 7.43 +/- 0.004 (despite arterial O2 saturation of 77%) after ascent from 3,600-4,100 to 5,260 m in 2 h. Maximal power output was similar in the two groups breathing air, whereas on 55% O2 only L showed a significant increase. During exercise in air, arterial PCO2 was 8 Torr lower in L than in N (P < 0.001), yet PO2 was the same such that, at maximal O2 uptake, alveolar-arterial PO2 difference was lower in N (5.3 +/- 1.3 Torr) than in L (10.5 +/- 0.8 Torr), P = 0.004. Calculated O2 diffusing capacity was 40% higher in N than in L and, if referenced to maximal hyperoxic work, capacity was 73% greater in N. Buffering of lactic acid was greater in N, with 20% less increase in base deficit per millimole per liter rise in lactate. These data show in L persistent alkalosis even after 9 wk at 5,260 m. In N, the data show 1) insignificant reduction in exercise capacity when breathing air at 5,260 m compared with breathing 55% O2; 2) very little ventilatory response to acute hypoxemia (judged by arterial pH and arterial PCO2 responses to hyperoxia); 3) during exercise, greater pulmonary diffusing capacity than in L, allowing maintenance of arterial PO2 despite lower ventilation; and 4) better buffering of lactic acid. These results support and extend similar observations concerning adaptation in lung function in these and other high-altitude native groups previously performed at much lower altitudes.

Acclimatization↗