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B W McKay

Publications and source records attributed to B W McKay.

4 recordsLinked to original sources
PubMed1999

Sternal acceleration ballistocardiography and arterial pressure wave analysis to determine stroke volume.

OBJECTIVE: To describe a cardiac output measurement using a new method to derive and analyze the long-axis ballistocardiogram that is less invasive than pulmonary artery thermodilution. DESIGN: Prospective physiologic study. SETTING: Intensive care unit of The Halifax Infirmary, a teaching hospital of Dalhousie University, Halifax, NS. PATIENTS: Thirty-nine patients in sinus rhythm with pulmonary artery thermodilution catheters or radial artery catheters in place. The first 30 subjects were the "learning set" and the next 9 were the "test set." INTERVENTIONS: A small (54-g) accelerometer was taped on the patient's chest. OUTCOME MEASURES: Measurements of time and amplitude coordinates of the acceleration and radial artery pressure wavepeaks, as well as anthropometric information. RESULTS: A stroke volume prediction equation was generated (R2 = 0.76) from the learning set. This equation was applied to the test set and correlated with the pulmonary artery thermodilution-derived stroke volumes (R = 0.79). Stroke volumes were compared using a previously described statistical method: a) bias (predicted > thermodilution) = 0.03 mL (95% confidence interval [CI] -4.2 to 4.8 mL); b) lower limit of agreement = -21 mL (95% CI -29 to -13 mL); c) upper limit of agreement = 22 mL (95% CI 14 to 29 mL). Of derived stroke volumes, 82% were within 15 mL of pulmonary artery thermodilution-derived values. CONCLUSIONS: The sternal acceleration ballistocardiogram combined with hemodynamic and demographic data in a probabilistic model shows promise of providing a less invasive measure of cardiac output than thermodilution.

Aged↗
PubMed1998

Resting muscle sounds in anesthetized patients.

It is known that contracting muscle makes low frequency sound vibrations. Small vibrations of uncertain origin are found over resting muscle. These could be shown to be of muscle origin if they significantly diminish in response to agents expected to decrease muscle activity. Thiopental, propofol, and neuromuscular-junction blocking muscle relaxants have such properties. Twenty-one subjects slated for elective surgery for which they would routinely be anesthetized and paralysed gave informed consent to having a small accelerometer taped upon their supine biceps (9 subjects), or volar forearm (12 subjects). Recordings were made in four stages while subjects: (i) lifted a 2-kg weight just off the sponge armrest on which their outstretched arm lay; (ii) relaxed their arm in the awake state prior to anesthesia; (iii) had anesthesia induced with intravenous thiopental (n = 11) or propofol (n = 10); and (iv) were paralysed. Recordings were digitised at 172-Hz and 6-s segments fast Fourier transformed (FFT). Total signal power, as determined by the area under the power spectrum, was significantly different (p < 0.05) in all stages for the biceps and in all but stages (iii) from (iv) in the forearm. It appears that resting muscle generates measurable vibrations.

Adolescent↗