Draw 3 separate graphs showing: (a) change in alveolar ventilation rate when the

Question

Draw 3 separate graphs showing: (a) change in alveolar ventilation rate when the H+ concentration in th cerebrospinal fluid surrounding cells in the brain stem is varied; (b) the change in ventaliation seen when moving from an alveolar PCO2 concentration from 40 to 46mmHg while maintaining alveolar oxygen constant at a PO2 of 100 mm Hg, and (c) the change in ventaliation seen when changing the alveolar PO2 from 60 to 100 mm Hg while keeping alveolar PCO2 constant at 38 mm Hg. Be sure to labe the axes!

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3. Draw 3 separate graphs showing: (a) change in alveolar ventilation rate when the cerebrospinal fluid surrounding cells in the brain stem is varied; (b) the change in ventila when moving from an alveolar PCO2 concentration from oxygen constant at a PO2 of 100 mm Hg, and (c alveolar PO2 from 60 to 100 mm Hg while keeping alveolar PCo2 constant at 38 mm Hg. Be sure to labe the axes! (4 points per graph; 12 points total) the H+ concentration in tion seen 40 to 46 mm Hg while maintaining alveolar e in ventilation seen when changing the ) the chang

Explanation / Answer

Effects of pH with constant Pco2 Attempts were made to alter pH of the superfusion fluid by modifying the HC03- concentration while the solution was equilibrated with 5 % CO2 in 02. As shown in Fig. 3A, a shift of pH to the acidic side by 0-25 units with constant PCO2 caused an increase in respiratory frequency as well as in respiratory magnitude (top two records). The bottom two curves in Fig. 3A show the changes in respiratory frequency and minute activity, respectively. In twelve preparations in which the pH was lowered by 0-25-0f30 units with constant Pco2, the respiratory frequency was increased, on the average, by 26 %, whereas the mean increase in minute activity was A 20 NaHCO3 10 NaHCO3 20 NaHCOC3 B 20 NaHCO3 60 NaHCO3 20 NaHCO3 5% C02 5% C02 5% C02 5% C02 5 % C02 5% CO 704 797.28 7 40 728 pH 0 s2pVs 2001 . 115 S*' 15 10 cr 200 ~~~~~~~~100 200 5 * 0 0 5 10 15 0 5 10 15 20 Time (min) Time (min) Fig. 3. A, effects of decreased pH with constant Pco1. Between the two arrows the perfusion solution was switched as indicated. Top trace, pH record. Second trace, the peak integrated value of phrenic discharge in each respiratory cycle. Upper curve, respiratory frequency per minute. Bottom curve, phrenic minute activity relative to the initial level. B, as A, but showing the effects of increased pH with constant Pco, 49 %. In eight preparations, the pH of the superfusion was increased by about 0 5 units with constant Pco, An example of these eight experiments is illustrated . In case (ApH = 0 52), the respiratory frequency was reduced by about 30 %, whereas the decrease in minute activity was about 45 %. In the eight experiments, the mean decrease in frequency was 41 %, and the mean decrease in minute activity was 51 %. Thus, respiratory changes induced by pH alteration with constant PCo2 are characterized by changes in both frequency and magnitude. In some preparations the changes in frequency were predominant, whereas in other preparations those in magnitude were predominant. It is not clear how the dominance of these changes in frequency or magnitude is determined in a given alternation of respiratory minute activity under varied pH with constant Poor Effects of CO2 at constant pH In the experiment illustrated .the preparation was superfused by solutions equilibrated with three different CO2 concentrations (2, 5 and 7 %) while the pH of every solution was maintained approximately at the same level (726-T730) by adjusting the HCO3- concentration. Respiratory magnitude was reduced in low PCO. (2%) and enhanced in high PCO2 (7 %) changes induced by varied PCO2 at constant pH were qualitatively different from those observed under altered pH with constant PCO2 in two aspects. First, respiratory changes occurring under the former condition were characterized by alterations in magnitude but not in frequency. Throughout the observation period ofthe experiment illustrated .for example, respiratory frequency did change in a range of 9-12/min, but these changes were not related to the Pco, level (C). On the other hand, the minute activity was clearly altered when the preparation was exposed to a new level of PCO2 . Secondly, respiratory changes occurred only transiently following alteration of PCO, at constant pH, subsiding to near-initial levels within 3-8 min while the preparation was still exposed to a new level of P O2..

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