Faculty Bibliography

First-breath ventilatory responses to graded inspiratory elastic and resistive loads were obtained from 80 women unfamiliar with respiratory experimentation. For each load 1) responses from different subjects ranged from a weak tidal volume defense coupled with an increased breathing frequency to a strong tidal volume defense coupled with a decreased frequency; 2) strong tidal volume defenders employed longer inspirations than did weak tidal volume defenders; and 3) individual respiratory frequency responses were mediated by changes in inspiratory and/or expiratory timing. Thus the group response was qualitatively the same as that reported for 80 men. Quantitatively, however, mean inspiratory airflow responses of women exceeded those of men by an amount attributable to women's higher intrinsic respiratory elastance. Tidal volume responses, on the other hand, did not differ significantly, suggesting that men and women produce different neural adjustments to loads. In support of this hypothesis, analysis of respiratory timing responses revealed that 1) men actively prolonged inspiration more than women during resistive loading; and 2) women actively shortened inspiration more than men during elastic loading. These findings indicate that the load-compensating behavior exhibited by men and women is similar but not identical

Ventilatory responses to inspiratory elastic and resistive loads of 67 men were analyzed. During the 1st, 5th, and 10th consecutively loaded breaths 1) individual responses ranged from a rapid-shallow to a slow-deep breathing pattern; 2) strong tidal volume (VT) defenders employed longer inspirations than did weak VT defenders; and 3) individual frequency responses were mediated by changes in inspiratory and/or expiratory timing. Thus the group response was qualitatively similar on the 1st, 5th, and 10th loaded breaths. Quantitatively, however, the group's mean minute ventilation increased throughout each episode owing to progressively larger tidal volumes coupled with equal breathing frequencies. During elastic loading this amplified VT defense was achieved by stronger inspirations with no systematic changes in timing, whereas during resistive loading it was achieved both by stronger and longer inspirations. Inspiring 5% CO2 induced a degree of hypercapnia exceeding that accompanying mechanical loading and yet elicited a comparatively modest enhancement of respiratory output. These findings suggest that in conscious humans 1) repeated mechanical loading activates neural load-compensating mechanisms; 2) the range of these neural adjustments varies with both load size and type; and 3) the stimulus to initiate this behavior is largely nonchemical

The upper body posture naturally adopted by long distance runners was quantified, and its effects on ventilation were assessed in 14 subjects. Maximum voluntary ventilation (MVV) and flow-volume loop maneuvers were performed in three seated positions: 1) natural running posture (RUN), with back angled forward 11 degrees, neck flexed, and head extended 35 degrees forward of the spinal column; 2) back vertical with head and neck as above (NEF); and 3) head and back vertical (VERT). MVV was significantly higher in RUN compared with both NEF and VERT, as were peak inspiratory pressure (PImax) from functional residual capacity, peak expiratory flow (PEF), and peak inspiratory flow (PIF). Expiratory flow at 50% of vital capacity was significantly higher in RUN and NEF than in VERT, consistent with reported increases in flow due to tracheal stiffening. The increased PIF and PImax in RUN indicate increased inspiratory muscle tension and/or improved transduction of tension into a more negative pleural pressure. Magnetometer tracings of rib cage dimensions demonstrated greater anteroposterior stability during maximal inspiratory efforts in RUN compared with VERT. The improved inspiratory function seen in RUN may be due to more effective diaphragmatic and/or accessory muscle function. These findings demonstrate that the position naturally adopted by long distance runners favors ventilation