Developmental patterns of heart rate and variability in infants with persistent apnea of infancy.

During periods of regular breathing, heart rate is slower and more variable in healthy (no history of respiratory distress syndrome) prematurely born infants with persistent apnea, relative to full-term control infants of comparable post-conceptional ages. We tested the hypothesis that the cardiovascular differences may be linked to the persistent apnea, rather than premature birth, by assessing heart rate and variability in full-term infants with persistent apnea. Thus, resting heart rate and variability were compared in full-term infants with apnea of infancy, prematurely born infants with persistent apnea, and full-term control infants.

Architectural and histochemical properties of cat hip 'cuff' muscles.

The architectural properties and fiber-type composition of the cat hip 'cuff' muscles, i.e. the deep layer of muscles encircling the hip joint, were determined.

Skeletal muscle fiber cross-sectional area: effects of freezing procedures.

The cross-sectional area (CSA) of individual fibers is an important measure of skeletal muscle plasticity. To investigate the effects of different freezing procedures on CSA measurements, the CSA of type-identified fibers in the cat tibialis anterior were determined following quick-freezing the muscle at a fixed physiological length (ipsilateral, frozen at length) and compared to the fiber CSA following quick-freezing a mid-portion of the muscle where the fibers were allowed to freely shorten during tissue preparation (contralateral, frozen as a block). The mean CSA of each fiber type was significantly smaller in the muscles frozen at length vs.