Left ventricular (LV) myocardial O2 extraction was studied in five healthy ponies which had catheters implanted in the great cardiac vein and main pulmonary artery 15-30 days before the study. The abdominal aorta was percutaneously catheterized to sample arterial blood. 2. In addition, phasic LV and aortic pressures, LV dP/dtmax and rate-pressure product were also studied; dP/dtmax is the maximal rate of rise of the left ventricular pressure during the isovolumic phase, and is considered an index of myocardial contractility. Measurements were made at rest (control) and during adenosine infusion (3 mumol kg-1 min-1) at rest, moderate exercise (heart rate 169 +/- 10 beats min-1), heavy exercise (heart rate 198 +/- 7 beats min-1), maximal exercise (heart rate 232 +/- 7 beats min-1), and adenosine infusion (3 mumol kg-1 min-1) during maximal exercise (heart rate 230 +/- 6 beats min-1). 3. In resting ponies, LV arterial to coronary venous O2 content difference (delta LVa-v O2) was 8.9 +/- 0.5 ml dl-1 and O2 extraction was 59.9 +/- 2.2%. Adenosine infusion at rest decreased delta LVa-v O2 and O2 extraction precipitously (2.6 ml dl-1 and 14.3 +/- 1.7%, respectively), thereby indicating superfluous LV myocardial perfusion. 4. Moderate, heavy and maximal exercise increased delta LVa-v O2 to 185, 194 and 218% of its control value and O2 extraction rose to 71 +/- 2, 75 +/- 1.5 and 78 +/- 0.9%, respectively. The widening of the delta LVa-v O2 gradient was due to the increased arterial O2 content during exercise. 5. Combining these observations with equine myocardial perfusion, the LV O2 consumption was calculated to be 7.8, 47.9 and 103.6 ml min-1 100 g-1 at rest, moderate and maximal exercise. In order to achieve the 13.4-fold increase in LV O2 consumption, the LV perfusion rose only 6-fold; the rest being met by widening the delta LVa-v O2. 6. Adenosine infusion during maximal exercise decreased delta LVa-v O2 and O2 extraction (10.7 +/- 1 ml dl-1 and 45%, respectively; P less than 0.0001). This indicated that coronary vasodilator capacity was not being completely expended in maximally exercising ponies. It is concluded that coronary circulation is unlikely to be a limiting factor to further exertion in ponies. Organ/tissue perfusion studies in exercising ponies have demonstrated that of all working muscles, the left ventricular (LV) myocardium received the highest level of blood flow.(ABSTRACT TRUNCATED AT 400 WORDS)
摘要
对5匹健康小马的左心室（LV）心肌氧摄取进行了研究，在研究前15 - 30天，已将导管植入大冠状静脉和主肺动脉。经皮穿刺腹主动脉采集动脉血样本。2. 此外，还研究了左心室和主动脉的相位压力、左心室dp/dtmax（等容相期间左心室压力的最大上升速率，被视为心肌收缩力指标）以及心率 - 压力乘积；在静息状态（对照）、静息时腺苷输注（3 μmol·kg⁻¹·min⁻¹）、中等强度运动（心率169 ± 10次/分钟）、剧烈运动（心率198 ± 7次/分钟）、最大运动（心率232 ± 7次/分钟）以及最大运动时腺苷输注（3 μmol·kg⁻¹·min⁻¹，心率230 ± 6次/分钟）期间进行测量。3. 在静息的小马中，左心室动脉至冠状静脉的氧含量差值（ΔLVa - v O₂）为8.9 ± 0.5 ml/dl，氧摄取率为59.9 ± 2.2%。静息时输注腺苷使ΔLVa - v O₂和氧摄取率急剧下降（分别降至2.6 ml/dl和14.3 ± 1.7%），从而表明左心室心肌灌注过多。4. 中等强度、剧烈和最大运动使ΔLVa - v O₂分别增加至对照值的185%、194%和218%，氧摄取率分别升至71 ± 2%、75 ± 1.5%和78 ± 0.9%。ΔLVa - v O₂梯度的扩大是由于运动期间动脉氧含量增加。5. 将这些观察结果与马的心肌灌注相结合，计算得出静息、中等强度和最大运动时左心室的氧消耗量分别为7.8、47.9和103.6 ml·min⁻¹·100 g⁻¹。为了使左心室氧消耗量增加13.4倍，左心室灌注仅增加了6倍；其余增加量通过扩大ΔLVa - v O₂来实现。6. 最大运动时输注腺苷降低了ΔLVa - v O₂和氧摄取率（分别为10.7 ± 1 ml/dl和45%；P < 0.0001）。这表明在进行最大运动的小马中，冠状血管舒张能力并未完全发挥。结论是，冠状循环不太可能是小马进一步运动的限制因素。对运动中的小马进行的器官/组织灌注研究表明，在所有工作肌肉中，左心室（LV）心肌接受的血流水平最高。（摘要截取自400字）
