Physiology
Cardiovascular
Which of the following best describes cardiac output:
Answer:
The cardiac output is the volume of blood pumped out of heart via the aorta per minute, Cardiac output (CO) = Stroke volume x Heart rate.CVS Systemic Overview
Physiology / Cardiovascular / Cardiac Output
Last Updated: 2nd May 2019
Definitions
The total blood volume in the circulatory system of a healthy adult is about 5 L.
The stroke volume is the volume of blood ejected per beat. It is usually about 70 mL/beat at rest.
The heart rate is the number of beats per minute. It is usually about 70 beats/minute at rest.
The cardiac output is the volume of blood pumped out of heart via the aorta per minute.
Cardiac output (CO) = Stroke volume x Heart rate = 70 mL/beat x 70 beats/min = 4900 mL/min
Therefore cardiac output is usually about 5 L/minute at rest in humans.
Mean Arterial Pressure (MAP)
During systole, the pressure in the left ventricle increases and blood is ejected into the aorta. The rise in pressure stretches the elastic walls of the aorta and large arteries and drives blood flow. Systolic pressure is the maximum arterial pressure during systole. During diastole, arterial blood flow is partly maintained by elastic recoil of the walls of large arteries. The minimum pressure reached before the next systole is the diastolic pressure. The difference between the systolic and diastolic pressure is the pulse pressure.
The mean arterial pressure (MAP) cannot be calculated by averaging these pressures, because for about 60% of the time, the heart is in diastole. It is instead estimated as the diastolic + one-third of the pulse pressure, e.g. = 80 + 1/3(110 - 80) = 90 mmHg where BP 110/80 mmHg.
Normal Pressures in the Circulation
The mean arterial pressure (MAP) at the start of the arterioles is about 65 mmHg. The pressure on the arterial side of capillaries is about 25 mmHg, and on the venous side is about 15 mmHg. Venules converge into veins and finally the vena cava. The pressure in the vena cava at the level of the heart (the central venous pressure) is usually close to 0 mmHg.
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- Biochemistry
- Blood Gases
- Haematology
| Biochemistry | Normal Value |
|---|---|
| Sodium | 135 – 145 mmol/l |
| Potassium | 3.0 – 4.5 mmol/l |
| Urea | 2.5 – 7.5 mmol/l |
| Glucose | 3.5 – 5.0 mmol/l |
| Creatinine | 35 – 135 μmol/l |
| Alanine Aminotransferase (ALT) | 5 – 35 U/l |
| Gamma-glutamyl Transferase (GGT) | < 65 U/l |
| Alkaline Phosphatase (ALP) | 30 – 135 U/l |
| Aspartate Aminotransferase (AST) | < 40 U/l |
| Total Protein | 60 – 80 g/l |
| Albumin | 35 – 50 g/l |
| Globulin | 2.4 – 3.5 g/dl |
| Amylase | < 70 U/l |
| Total Bilirubin | 3 – 17 μmol/l |
| Calcium | 2.1 – 2.5 mmol/l |
| Chloride | 95 – 105 mmol/l |
| Phosphate | 0.8 – 1.4 mmol/l |
| Haematology | Normal Value |
|---|---|
| Haemoglobin | 11.5 – 16.6 g/dl |
| White Blood Cells | 4.0 – 11.0 x 109/l |
| Platelets | 150 – 450 x 109/l |
| MCV | 80 – 96 fl |
| MCHC | 32 – 36 g/dl |
| Neutrophils | 2.0 – 7.5 x 109/l |
| Lymphocytes | 1.5 – 4.0 x 109/l |
| Monocytes | 0.3 – 1.0 x 109/l |
| Eosinophils | 0.1 – 0.5 x 109/l |
| Basophils | < 0.2 x 109/l |
| Reticulocytes | < 2% |
| Haematocrit | 0.35 – 0.49 |
| Red Cell Distribution Width | 11 – 15% |
| Blood Gases | Normal Value |
|---|---|
| pH | 7.35 – 7.45 |
| pO2 | 11 – 14 kPa |
| pCO2 | 4.5 – 6.0 kPa |
| Base Excess | -2 – +2 mmol/l |
| Bicarbonate | 24 – 30 mmol/l |
| Lactate | < 2 mmol/l |
