Normal Physiological Parameters
Normal physiological parameters are standardized ranges of measurements that represent healthy bodily functions in individuals, with specific values varying based on age, sex, and other demographic factors. 1
Cardiovascular Parameters
- Heart Rate: Normal resting heart rate is typically 50-80 beats per minute, with a maximum heart rate calculation of 202 - 0.72(age) 1
- Blood Pressure: Systolic blood pressure rises with increasing dynamic work as cardiac output increases, while diastolic pressure typically remains about the same or moderately lower 1
- Oxygen Pulse: Normal values are calculated as 0.28(height) + 3.3(sex) + 26.7, with sex coded as 1 for males and 0 for females 1
- Fractional Flow Reserve (FFR): Normal value is 1.0 for every patient and every coronary artery, with values ≤0.75 associated with inducible ischemia and values ≥0.80 indicating absence of inducible ischemia 1
Respiratory Parameters
- Maximum Inspiratory Pressure (MIP): Lower limits of normal are 75 cm H₂O for men and 50 cm H₂O for women 2
- Maximum Expiratory Pressure (MEP): Lower limits of normal are 100 cm H₂O for men and 80 cm H₂O for women 2
- Chest Wall Compliance: Varies with age, ranging from approximately 5.7 ml/cm H₂O in preterm infants to 350 ml/cm H₂O in adults aged 20-29 years, decreasing to 210 ml/cm H₂O in adults aged 70-79 years 1
- Minute Ventilation: Normal value calculated as 26.3(VC) + 34, where VC is vital capacity 1
Metabolic Parameters
- Peak Oxygen Uptake (VO₂ max): Normal values range from approximately 80 ml O₂·kg⁻¹·min⁻¹ in young elite athletes to 15 ml O₂·kg⁻¹·min⁻¹ in apparently healthy 80-year-old females 1
- Anaerobic Threshold: Normally occurs at approximately 50-65% of peak VO₂ 1
- Respiratory Exchange Ratio: Peak value ≥1.10 is widely accepted as indicating excellent exercise effort 1
- Body Mass Index (BMI): Normal weight is defined as BMI 18.5-24.9 kg/m² 3
Age and Sex Considerations
- Age-Related Changes: Normal physiological parameters show predictable changes with age, such as decreases in maximum heart rate, VO₂ max, and chest wall compliance 1
- Sex Differences: Many parameters show significant differences between males and females, with males typically having higher values for respiratory muscle strength, oxygen uptake, and cardiac output 1, 2
- Pediatric Values: Children have distinct normal ranges that change with growth and development, requiring age-specific reference values 1, 4
Clinical Applications and Pitfalls
- Reference Value Limitations: Reference values show the range of average values in healthy populations but do not necessarily determine or predict present and future health status 5
- Measurement Variability: Physiological parameters can be affected by measurement techniques, patient effort, and environmental conditions 2, 6
- Population Differences: Some parameters may vary by ethnicity and geographic location, such as BMI thresholds for health risks being lower in Asian populations 3, 4
- Individual Variation: Wide normal ranges reflect natural variation between individuals, making it important to consider trends and changes from baseline in addition to absolute values 2, 7
Special Considerations
- Exercise Testing Preparation: For accurate measurement during exercise testing, subjects should not eat or smoke for 3 hours before testing, avoid unusual physical efforts for at least 12 hours, and dress appropriately 1
- Medication Effects: Some medications (especially β-blockers) can attenuate exercise responses and limit test interpretation 1
- Environmental Factors: Barometric pressure affects normal values for pulmonary gas exchange parameters 1
Understanding normal physiological parameters is essential for distinguishing between health and disease states, but interpretation must consider individual factors, measurement conditions, and the specific clinical context.