The first part of my work evaluates bilateral supramaximal transcutaneous phrenic nerve stimulation as a diagnostic test for respiratory muscle fatigue. I found that twitch transdiaphragmatic pressure (Pdi,T) was inversely and linearly related to lung volume (V$ sb{ rm L}$) both before and after fatigue. Although fatigue caused significant decrease in Pdi,T amplitude at all V$ sb{ rm L}$, the fractional decrease in Pdi,T was greater at high V$ sb{ rm L}$, indicating the importance of V$ sb{ rm L}$ as an independent variable that needs to be controlled whenever Pdi,T is determined. Twitch mouth pressure (Pm,T) was found to be linearly related to twitch esophageal pressure (Pes,T), to Pdi,T, and to V$ sb{ rm L}$. All these relationships were reproducible. Diaphragmatic fatigue resulted in significant decrease in Pm,T proportional to the decrease in Pdi,T for a given V$ sb{ rm L}$ so that Pm,T-Pes,T and Pm,T-Pdi,T relationships were unchanged. Thus the Pm,T-V$ sb{ rm L}$ relationship can be used to assess diaphragmatic fatigue non-invasively. Paired phrenic nerve shocks which were well tolerated by normal subjects can be used to obtain a measure of the pressure-frequency curves of the diaphragm, which were reproducible. In particular, I showed that the pressure ratio of diaphragmatic twitch elicited by the second shock at 10Hz over that at 100Hz (T2$ sb{10/100}$) is a valuable index of low frequency fatigue. / In the second part of my work I studied the effect of respiratory muscle fatigue on ventilatory response to CO$ sb2$ and respiratory muscle recruitment. The data showed that ventilatory response and respiratory muscle recruitment patterns were different in a number of aspects between diaphragmatic fatigue and global inspiratory muscle fatigue. After diaphragmatic fatigue, the only change was an increase in the recruitment of rib cage muscles, which fully compensated for decreased diaphragmatic contractility because all the ventilatory parameters were constant. After global fatigue, both the diaphragm and rib cage muscles contributed less to breathing but expiratory muscles were recruited resulting in a decrease in end-expiratory P$ sb{ rm L}$ and an increased contribution of elastic energy stored within the respiratory system to inspiratory tidal volume generation. In spite of this, rapid shallow breathing developed while minute ventilation remained constant. These data suggest that the ventilatory control system can detect fatigue and has sufficient plasticity to alter inspiratory drive appropriately. The overall ventilation level can thus be maintained.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.41180 |
| Date | January 1993 |
| Creators | Yan, Sheng |
| Contributors | Macklem, Peter T. (advisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Division of Experimental Medicine.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001327503, proquestno: NN87957, Theses scanned by UMI/ProQuest. |
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