Signals consistent with microbubbles detected in legs of normal human subjects after exercise

Abstract

Exercise may produce micronuclei (presumably gas-filled bubbles) in tissue, which could serve as nucleation sites for bubbles during subsequent decompression stress. These micronuclei have never been directly detected in humans. Dual-frequency ultrasound (DFU) is a resonance-based, ultrasound technique capable of detecting and sizing small stationary bubbles. We surveyed for bubbles in the legs of six normal human subjects (ages 28-52 yr) after exercise using DFU. Eleven marked sites on the left thigh and calf were imaged using standard imaging ultrasound. Subjects then rested in a reclining chair for 2 h before exercise. For the hour before exercise, a series of baseline measurements was taken at each site using DFU. At least six baseline measurements were taken at each site. Subjects exercised at 80% of their age-adjusted maximal heart rate for 30 min on an upright bicycle ergometer. After exercise, the subjects returned to the chair, and multiple postexercise measurements were taken at the marked sites. Measurements continued until no further signals consistent with bubbles were returned or 1 h had elapsed. All subjects showed signals consistent with bubbles after exercise at at least one site. The percentage of sites in a given subject showing signals significantly greater than baseline (P < 0.01) at first measurement ranged from 9.1 to 100%. Overall, 58% of sites showed signals consistent with bubbles at the first postexercise measurement. Signals decreased over time after exercise. These data strongly suggest that exercise produces bubbles detectable using DFU.

Immediate non-traumatic postmortem computed tomographic demonstration of myocardial intravascular gas of the left ventricle: effects from cardiopulmonary resuscitation

“…Gas nuclei grow to become visible, and stable gas bubbles depend on the dissolved CO 2 gas concentration (Wilbur et al 2010; Lin et al 2000). Partial venous pressure of CO 2 ( P vCO 2 ) elevates during CPR and its causes are as follows (Suwa 1992; Halmagyi et al 1970; Suwa et al 1969; Chazan et al 1968; Weil et al 1986; Gudipati et al 1990; Lindner et al 1991): 1) increased arterial-venous difference of P CO 2 due to low cardiac output, 2) increased CO 2 production due to anaerobic metabolism progression, and 3) decreased CO 2 transport by the blood.…”

“…Second, PMCT findings could not morphologically differentiate whether the myocardial intravascular gas of the LV was in the artery or in the vein. However, tribonucleation and supersaturation of CO 2 , which are the two predominant theories of gas nuclei and bubbles origin (Wilbur et al 2010; Lin et al 2000), suggest that the gases were in the vein. Additionally, the presence of intravascular gas in the venula of pericardial fat may be indirect evidence.…”

Pre-Dive Exercise and Post-Dive Evolution of Venous Gas Emboli

“…The question remains as to why cycling exercise did not produce benefi cial results. In a recent study carried out by Wilbur et al ( 31 ), a dual frequency ultrasound technique was used to detect microbubbles in the legs of subjects before and after cycling exercise. This technique would be useful to compare the amount of bubbles produced by different types of exercise and, in this case, Wilbur's results suggested that cycling did produce an increased amount of detectable microbubbles.…”

Tribonucleation of bubbles

“…It has been known for at least half a century that, as noticed by Hayward in 1967 (11), "extremely gentle rubbing" of two solid objects inside a liquid under tension, which is otherwise stable against most forms of mechanical action (e.g., knocking on the container wall or stirring), readily induces nucleation. This tribonucleation is often cited as a plausible source of the microbubbles found in the limbs of humans and animals after physical exercise (12,13). Campbell (14) and Ikels (15) attributed the nucleation observed in these conditions to the pressure drop induced by the viscous flow in the space between two separating solid surfaces.…”