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Biomedical subjects

A J Mortimer

Publications and source records attributed to A J Mortimer.

47 records · Page 3Linked to original sources
PubMed1984

Effect of brief ultrasound exposure on post-tetanic potentiation in cardiac muscle.

The effect of a short 4 second ultrasound application (1.0 W/cm2 sATA at 963 KHz) on the post-tetanic-potentiation of isolated isometrically contracting rat papillary muscle has been evaluated. Post tetanic-potentiation was produced in hypoxic isolated papillary muscle by interrupting the control stimulation rate of 6/minute with 10 stimulating pulses at 0.2 sec intervals for one cycle. Ultrasound application varied from one second prior to the stimulating train to a period covering the entire train. Ultrasound application just preceding and impinging upon the pulse train, enhanced post-tetanic-potentiation contractions. However, delay in ultrasound application and covering the stimulating pulse train, reduced post-tetanic-potentiation contractions. These data suggest that a window exists for the effects of ultrasound on contracting myocardium which may be used to probe critical events in the cardiac cycle.

Animals↗
PubMed1984

Measurement of lung volume by multiple indicator dilution. A simple model and its ramifications.

A simple, idealized rebreathing manoeuvre was simulated numerically on a Hewlett-Packard 9825A desk-top calculator. Approximate imitations were obtained of real-life observations of differences between apparent volumes of distribution of different indicators in the same rebreathing manoeuvre. The simulated patterns of discrepancy depended heavily on the uptake or output profiles which were assumed for carbon dioxide and nitrous oxide during the hypothetical rebreathing manoeuvres. The simulations pointed to the analytical algebraic expressions which explained the simulated patterns of discrepancy. A procedure was devised to correct for the effects of these uptakes or outputs. It depended on considering the mixing of oxygen, nitrogen and argon as if it were occurring in a separate part of the rebreathing system occupied only by these gases. The volume of this notional part would decrease linearly with time at a rate equal to the oxygen consumption.

Argon↗
PubMed1980

A relationship between ultrasonic intensity and changes in myocardial mechanics.

The effects of ultrasound on the mechanical properties of isometrically contracting rat papillary muscle have been studied as a function of the intensity of the ultrasonic irradiation. Each muscle was subjected to irradiation at 1.1., 2.2, and 3.3 W/cm2 at a frequency of 2.3 MHz. Ultrasonic irradiation caused heating in the vicinity of the muscle; thus it was necessary to separate the pure thermal and ultrasonic effects. After irradiation the bath temperature was increased so that the muscle reached the same temperature which occurred during ultrasonic irradiation. The mechanical parameters measured during the equivalent thermal procedure were compared with the parameters during irradiation. There was a significant (p less than 0.05) decrease in resting force which was significantly different from the equivalent thermal intervention and could be related to the ultrasonic intensity. Thus, the effect of ultrasound on rat papillary consists of two components, a thermal component which affects all parameters studied and a nonthermal component which affects only the diastolic force.

Animals↗
PubMed1979

Clinical evaluation of an inexpensive ultrasound oculometer for ocular biometry.

We measured anterior chamber depth and axial length in 200 human eyes with the Echo-Oculometer and the Digital Biometric Ruler. There was good agreement between measurements with the two instruments. The echo-Oculometer is much less expensive than any other instrument available for measuring ocular axial length and satisfactorily provides information for calculation of power of intraocular lenses.

Anterior Chamber↗
PubMed1978

The effects of ultrasound on the mechanical properties of rat cardiac muscle.

The mechanical properties of cardiac muscle during ultrasonic irradiation have been studied in vitro. Left anterior papillary muscle from normal rats was suspended in buffered lactated Ringers solution equilibrated with 95% O2, and 5% CO2 and maintained at 20 degrees C. The muscles were stimulated to contract isometrically three times per minute at the length which produced maximum tension. Each muscle was irradiated with a MHz ultrasound at an average power of 2.4 Wcm-2 for a period of 10 min with a 10 min recovery period. Irradiation caused an average increase in temperature of the muscle of 1.7 +/- 0.2 degrees C (mean +/- SEM). Irradiation caused the resting tension (1.46 +/- 0.13g) to decrease by 17.8 +/- 4.7% and the developed tension (3.33 +/- 0.61g) to decrease by 4.1 +/- 0.9%. Since changes in contractile properties have been reported with temperature the bath temperature was raised and changes in contraction observed. When compensated for effects of temperature, the changes in resting tension became - 13.3 +/- 4.1% while the change in developed tension became + 1.6 +/- 2.3%. The change in resting tension is highly significant (p less than 0.05 paired t-test) while the change in developed tension is not. Thus 1 MHz ultrasound at an intensity of 2.4 Wcm-2 appears to affect resting tension of cardiac muscle without affecting the active tension. Since changes in cardiac mechanics of this type have not been described previously the effects of ultrasound appears to be unique.

Animals↗
PubMedDate not supplied

Ultrasound intensity and contractile characteristics of rat isolated papillary muscle.

The effect of graded intensities of continuous wave ultrasound on the contractile performance of isolated papillary muscle of rat was tested. Under isometric conditions rat left ventricular papillary muscles (n = 48) were electrically stimulated to contract at rates of 30, 60, 120 and 240 beats per minute. Muscles were perfused with a Tyrode solution at 30 degrees C under normoxic conditions. Ultrasound at intensities of 0.25, 0.50, 1.0 and 2.0 W/cm2 spatial average temporal average (SATA) at 963 kHz was applied to the muscles while recording muscle contractile characteristics. The analog data were digitized and stored on disk for analysis by computer. This revealed a significant (p less than 0.001) increase in peak developed force (F), peak rate of force development (+dF/dt) and peak rate of myocardial relaxation (-dF/dt) that was linearly related to ultrasound intensity. The muscles were more sensitive to ultrasound at 240 contractions per minute. Resting force was significantly decreased by ultrasound. Although bath temperature increased according to the ultrasound intensity, control studies in papillary muscles (n = 24) on the correlation between contractile parameters and temperature revealed that bulk heating could not account for the positive inotropic action with ultrasound. These data confirm the inotropic effect of continuous wave ultrasound on myocardial tissue and point to the possibility of applying this phenomenon therapeutically.

Animals↗