We measured rat left ventricular pressure, volume, and oxygen consumption ( = arteriovenous oxygen content differencexcoronary flow) to establish a new evaluation of its mechanoenergetics in the whole heart preparation by using the cross-circulation method. We obtained a curved end-systolic pressure-volume relation in contrast to a linear end-systolic pressure-volume relation in dogs, rabbits, and humans. However, we obtained a linear oxygen consumption per beat (VO2)-systolic pressure-volume area (PVA, a measure of left ventricular total mechanical energy per beat) relation as in other species. Thus PVA can be a good index for assessing rat left ventricular mechanoenergetics. The VO2 intercept and slope of the linear VO2-PVA relation correspond to those in other species. Intracoronary calcium elevated the curved end-systolic pressure-volume relation and significantly increased PVA at 0.15 ml/g of left ventricular end-diastolic volume (PVA0.15) by 50%. Calcium also significantly increased the VO2 intercept of the VO2-PVA relation by 30% without a change in its slope. We conclude that the rat left ventricular end-systolic pressure-volume relation is curved, but the VO2-PVA relation is linear, and that the VO2 intercept is mainly composed of PVA-independent VO2, presumably VO2 for Ca2+ handling in the excitation-contraction coupling and basal metabolism. Therefore we propose PVA at an appropriate left ventricular volume and the VO2 intercept as good rat left ventricular mechanoenergetic indexes despite the nonlinearity of the end-systolic pressure-volume relation.
Object. The goal of this study was to investigate outcomes in patients with vestibular schwannoma (VS) who were treated with fractionated stereotactic radiotherapy (SRT).
Methods. One hundred one patients with VS were treated with fractionated SRT at a radiation level of 40 to 50 Gy administered in 20 to 25 fractions over a 5- to 6-week period. The median tumor size in these patients was 19 mm (range 3–40 mm), and 27 tumors were larger than 25 mm. Patients were consistently followed up using magnetic resonance imaging every 6 months for 5 years in principle. The median follow-up period was 45 months. The actuarial 5-year rate of tumor control (no growth > 2 mm and no requirement for salvage surgery) was 91.4% (95% confidence interval 85.2–97.6%). Three patients with progressive tumors underwent salvage tumor resection. The actuarial 5-year rate of useful hearing preservation (Gardner—Robertson Class I or II) was 71%. The observed complications of fractionated SRT included transient facial nerve palsy (4% of patients), trigeminal neuropathy (14% of patients), and balance disturbance (17% of patients). No new permanent facial weakness occurred after fractionated SRT. Eleven patients (11%) who had progressive communicating hydrocephalus (cerebrospinal fluid malabsorption) and no evidence of tumor growth after fractionated SRT required a shunt. The symptoms of this type of hydrocephalus were similar to those of normal-pressure hydrocephalus and occurred 4 to 20 months (median 12 months) after fractionated SRT. The mean size (± standard deviation) of tumors causing symptomatic hydrocephalus (25.5 ± 7.8 mm) was significantly larger than that of other tumors (18.2 ± 8.7 mm) (p = 0.011). Only four of the 72 patients with tumors smaller than 25 mm in maximum diameter received a shunt.
Conclusions. Fractionated SRT resulted in an excellent tumor control rate, even for relatively large tumors, and produced a high rate of hearing preservation that was comparable to the best results of single-fraction radiosurgery. The progression of communicating hydrocephalus should be monitored closely, particularly in patients harboring a large VS.
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