Normal asynchrony of left ventricular long and short axes: their relationship with aortic hemodynamics.

BACKGROUND: The relationship between left ventricular (LV) long and short axes, aortic pressure (P), flow velocity (U) and wave intensity is not well established. METHODS: Eleven dogs were anaesthetized and mechanically ventilated and LV long and minor axes shortening velocities were calculated using ultrasound crystals. P and U were measured in the ascending aorta using a high fidelity pressure catheter and ultrasonic flow transducer. RESULTS: Pre-ejection: The LV minor axis began to shorten as the long axis lengthened creating LV shape change. Early ejection: The aortic valve opened 83+/-20 ms after the ECG Q-wave. Aortic P and U simultaneously increased; peak aortic velocity and maximum minor axis shortening velocity (M(max)) occurred at 152+24 and 147+24 ms, respectively; p=0.66, intra-class correlation ICC 0.93). M(max) also corresponded to the time when the reflected compression wave arrived back to the heart (ICC 0.75). Late ejection: LV long axis reached its peak shortening velocity 28+21 ms later than the minor axis at 175+/-33 ms, coinciding with peak LV pressure (187+25 ms; p=0.77, ICC 0.65) and onset of the forward expansion wave (177+28 ms, p=0.88, ICC 0.89). Both axes then continued to slow until 210+/-30 ms when an increased rate of decline of shortening velocity corresponded with peak aortic pressure. CONCLUSION: Long axis peak shortening velocity lagged consistently behind the minor axis, representing a degree of normal asynchrony. The arrival of the reflected wave appears to bring about the slowing down of the minor axis.

Problems in the measurement of functional residual capacity.

Accurate assessment of lung volume in infancy is important to determine the impact of disease and the efficacy of therapies. A new generation of infant plethysmographs with lower apparatus deadspace has been produced, but gives lower volume results than those from older traditional plethysmographs. We hypothesized that the new plethysmographs might have greater sensitivity to the adiabatic effect and hence they, rather than the traditional plethysmographs, produced erroneous results. Our aim was to assess the influence of the adiabatic effect on the results of a contemporary plethysmograph, an older traditional plethysmograph and a helium gas dilution system using a lung model. Altering the amount of copper wool within the lung model allowed the influence of the adiabatic effect on the plethysmographic results to be assessed. The measured compared to the actual volumes were significantly lower for the contemporary plethysmograph compared to the traditional plethysmograph (p < 0.001) and to the helium gas dilution system (p < 0.001). Under optimal testing conditions the contemporary plethysmograph under-recorded by 11-13%, whereas the other two systems gave similar results to the actual volumes. As the effect of the adiabatic effect was increased, the discrepancy between the results of the contemporary and the traditional plethysmographs increased. We conclude, the contemporary plethysmograph is more sensitive to adiabatic effects and hence under-records.