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Article Title

VENTILATORY RESPONSES TO ADDED EXTERNAL DEAD SPACE WITH VARYING RESISTANCE DURING EXERCISE

Abstract

When additional dead space is added externally to the respiratory system, research has shown that minute ventilation increases. How this is accomplished has yet to be fully characterized; whether it is an increase in tidal volume, respiratory rate or both. Also, the effect of added resistance to the respiratory airflow has been investigated and it was found that tidal volume increased to maintain adequate ventilation. To date, it doesn’t appear any studies have examined the combination of added dead space and resistance together and its effect on ventilation during exercise. PURPOSE: The purpose of this study was to examine the respiratory response to added external dead space with varying resistances during submaximal exercise. METHODS: Fourteen male subjects, (height: 175-188 cm, age: 19-22 yrs) completed three 10 minute bouts of submaximal exercise at 100 W on a cycle ergometer with the breathing apparatus modified to create three different external dead space configurations. In the first condition, which was the baseline (B), no external dead space was added. During the other two conditions, 800 mL of external dead space was added to the breathing apparatus via tubing, the resistance was varied by changing the diameters of the tubing from 33 mm for the dead space condition (DS), to 25 mm for the resistance plus dead space condition (R+DS). Throughout each 10 minute period of exercise, rate of oxygen consumption (VO2), respiratory rate (RR), tidal volume (VT), end-tidal partial pressure of oxygen and carbon dioxide (PETO2, PETCO2), and minute ventilation(VE) were collected using a metabolic cart. True values (i.e. lung values) for PETO2, PETCO2, PIO2, and PICO2 were then estimated using equations 1-4 which took into account the added dead space. Measured variables were compared between conditions using repeated-measures ANOVA. The level of significance was set at p<0.05. RESULTS: An increase was seen in VT (2.16±.38 to 2.51±.28 L), RR (20.98 ± 3.35 to 24.2±3.7 bpm), VE (33.4 ± 4.5 to 45.72±5.69L/min), and PETO2 (110.3 ± 2.5 to 120.3±2.3mmHg), while PETCO2 (33.4± 2.13 to 23.81±1.7mmHg) decreased when going from B to DS (p<0.05), but with the addition of resistance there was no further change. No differences were observed in VO2 (1.82 ± .14) and VCO2 (1.56 ± .13) between trials. The adjusted values of PICO2 (and PECO2) significantly increase from B to DS condition but did not increase further with the addition of resistance (p<0.05). PIO2 decreased when going to a DS condition but PEO2 had no change between trials (p<0.05) CONCLUSIONS: This study found that when trying to decrease the impact on breathing that an apparatus may have it is better to try and reduce the amount of dead space that a system has than to try and reduce the resistance.

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