Most health content online is written to rank, not to help. These articles are written by a board-certified family medicine physician for the patients she actually sees — adults and seniors in Miami-Dade County managing real conditions, real insurance, and real schedules.
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Health Blog in Miami, FL
The health blog from Lisette Portes, MD, a board-certified primary care doctor in Miami, FL, publishes patient-focused articles on chronic pain management, type 2 diabetes, high blood pressure, annual physicals, women's health, senior and Medicare care, weight loss, and preventive screening for adults across Miami-Dade County.
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Articles are organized by category below and updated as guidelines change.
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Primary Care and Prevention
Chronic Pain
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Heart Health and Blood Pressure
Women's Health
Senior Health and Medicare
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October 2026
Autonomic Nervous System and Heart Rate Variability
Patient and clinician articles on autonomic physiology, HRV measurement, symptoms, sleep, stress, exercise, and chronic disease.
What Is the Autonomic Nervous System, and How Does It Shape Your Health?
The autonomic nervous system (ANS) is the part of your nervous system that runs automatic body functions, including heart rate, blood pressure, breathing, digestion, sweating, bladder control, and pupil size. Its sympathetic branch prepares you for action, its parasympathetic branch supports rest and repair, and its enteric branch manages the gut. Because it links every organ, ANS balance shapes sleep, stress, heart rate variability, and chronic disease.
Read articleAutonomic Dysfunction Symptoms: How Can You Tell If Your Nervous System Is Dysregulated?
Autonomic dysfunction symptoms include lightheadedness when standing, a racing heart, fatigue, brain fog, digestive upset, abnormal sweating, and bladder changes. Doctors confirm a problem with orthostatic vital signs, symptom questionnaires, and sometimes formal autonomic testing, not by symptoms alone. Common causes include POTS, orthostatic hypotension, and diabetic neuropathy. Learn how the autonomic nervous system works and how chronic disease management addresses underlying causes.
Read articleWhat Is Heart Rate Variability, and What Does Your HRV Reveal About Your Health?
Heart rate variability (HRV) is the natural, millisecond-level variation in time between consecutive heartbeats, and it mainly reflects how flexibly your autonomic nervous system adjusts heart rhythm. Higher resting HRV usually signals strong vagal regulation. HRV is a useful trend marker for sleep, stress, and recovery, but it is not a diagnosis on its own. See normal HRV ranges by age or talk with a primary care physician.
Read articleNormal HRV by Age: What Counts as a Good Heart Rate Variability for You?
Normal HRV by age has no single cutoff, because values depend on age, sex, fitness, the metric, and the device. HRV generally declines with age. In a 1998 Holter study by Umetani and colleagues, average 24 hour RMSSD fell from 43 ms in people in their 20s to 25 ms in their 50s. Your own trend matters more than any chart. Learn what HRV measures and what low HRV means.
Read articleWhat Does a Low HRV Mean, and When Is It a Real Concern?
A low HRV usually means your nervous system is under short-term strain from poor sleep, alcohol, illness, stress, or hard training, and it often recovers within days. A persistently low HRV, measured over time, is linked with higher cardiovascular risk. Learn the basics in our heart rate variability guide, compare normal HRV by age, and see how the autonomic nervous system ties it together.
Read articleHow Poor Sleep Changes Your Nervous System: Sleep and HRV Explained
Poor sleep shifts the autonomic nervous system toward fight or flight activity, which raises heart rate and lowers HRV, while healthy deep sleep is the most restful state for the heart. Sleep and HRV are closely tied, and sleep apnea and alcohol are common disruptors. Read our autonomic nervous system guide and learn what a low HRV means.
Read articleHow Chronic Stress Changes Your Autonomic Balance: Understanding Stress and the Nervous System
Chronic stress affects the autonomic nervous system by keeping the sympathetic "fight or flight" branch switched on and weakening the calming parasympathetic, or vagal, branch. Understanding stress and the nervous system helps explain why long-term stress is linked to lower heart rate variability, higher blood pressure, poor sleep, and digestive problems. Start with the autonomic nervous system and heart rate variability.
Read articleHow Exercise Changes Heart Rate Variability and Autonomic Function: A Guide to Exercise and HRV
Exercise affects heart rate variability in two ways: a single hard workout temporarily lowers HRV while the body recovers, and consistent training over weeks tends to raise resting HRV and strengthen vagal tone. Understanding exercise and HRV helps you balance effort and rest. Learn the basics of heart rate variability, the autonomic nervous system, and normal HRV by age.
Read articleHow Autonomic Dysfunction and Chronic Disease Are Connected in the Body
Autonomic dysfunction and chronic disease are closely linked because the autonomic nervous system regulates blood pressure, heart rate, glucose, digestion, and inflammation. Research shows sympathetic overactivity in hypertension, obesity, heart failure, and kidney disease, while diabetes can damage autonomic nerves directly. Start with our guide to the autonomic nervous system and learn how chronic disease management can address these connections.
Read articleHRV Interpretation in Clinical Practice: Metrics, Pitfalls, and Evidence-Based Uses
HRV interpretation in clinical practice depends on method. The 1996 Task Force standards recommend 5-minute stationary recordings for spectral analysis and nominal 24-hour recordings for time-domain analysis, and the two should not be compared. RMSSD and HF power best reflect vagal modulation, LF/HF is not a reliable sympathovagal index, and HRV is a risk marker rather than a diagnosis. See our HRV overview and normal HRV ranges.
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