Forces associated with head lifting efforts as well as mouth pressure were measured on four supine normal men, at five different lung volumes from FRC to TLC, and with the head positioned at two different heights above the bed. Positioning the head at one of the two heights (3cm and 10cm) provided for a change in length of the sternocleidomastoid (SCM) muscle. Graded efforts of head lift, and graded inspiratory pressure manoeuvres were executed and corresponding electromyograms of the SCM were measured. The mass lifted during efforts of head lift under static conditions (HSL) was measured with a self-contained transducer system located under the head of the subject. The muscle pressures at different lung volumes were obtained from pressure transducer records by adding the pressure-volume relaxation curve to the inspiratory mouth pressure-volume curve. The electromyogram of the SCM was obtained from surface electrodes, amplified and processed with a smoothing integrator to obtain the mean rectified electromyogram (MRE). For every subject, the relationships between MRE and MASS LIFTED, and between MRE and MUSCLE PRESSURE were linear for every lung volume at every head height above the bed ( r² >0.95 ). Data from all subjects were put together to form a single linear relationship (MRE vs MASS LIFTED and MRE vs MUSCLE PRESSURE) for every head height above the bed. The variability was greater at 3cm than at 10cm of head height. For both the head lift manoeuvre and the respiratory manoeuvre, there was a greater variability due to lung volume, on the slope and intercept of the curves at 3cm, than at 10cm of head height. Furthermore, more EMG was generated at 10 cm than at 3cm for a constant mechanical output, i.e., head lift or muscle pressure. Statistical tests were performed on the curves. Slope and intercept of the curves at different lung volumes, for a specific manoeuvre and head height above the bed were not significantly different ( p<0.05 ). The curves at different lung volumes were then put together to form a single linear relationship for both manoeuvres at both heights. Slope and intercept of the "pooled" curves, at both 3cm and at 10cm, were tested for both head lift and respiratory manoeuvres. It was found that the slopes were significantly different ( p<0.05 ) while the intercepts were net. Using the input variable, MRE, as the common factor, a linear relationship between the two output variables, MASS LIFTED and MUSCLE PRESSURE, was determined at each head height. Interpretation of the resulting relationships shows that: (a) About 50% of the maximum inspiratory muscle pressure can be generated without using the SCM muscle. (b) For the head located at 3cm above the bed, the production of muscle pressure from 50% to 100% Pmusc(max) corresponds to lifting, with the head, a mass equivalent to 4.5 times the head mass, while at 10cm above the bed, the same respiratory manoeuvre corresponds to lifting a mass equal to 1.3 times the head mass. (c) Changes in lung volume do not bring about as great changes in length of the SCM muscle as do changes in head height. / Thesis / Master of Engineering (ME)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22993 |
| Date | 04 1900 |
| Creators | Lemieux, D. |
| Contributors | Pengelly, L., Engineering Physics |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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