MEDREH · EP 07 · GERIATRICS
Before You Listen
Episode Setup
- Topic in one line: the age-associated physiologic changes (sarcopenia, declining cardiac and pulmonary reserve, altered pharmacokinetics), evidence-based fall risk assessment with the Timed Up and Go (TUG) / Berg Balance Scale / Tinetti Performance-Oriented Mobility Assessment thresholds, the Beers Criteria for potentially inappropriate medications, hip fracture classification and post-operative protocols, the Fried frailty phenotype, the Confusion Assessment Method (CAM) for delirium, and the four major dementia subtypes that drive American Board of Physical Medicine and Rehabilitation (ABPMR) Part I geriatric questions.
- Prerequisites: basic muscle fiber types (Type I slow-twitch, Type II fast-twitch), hepatic phase I cytochrome P450 metabolism vs phase II conjugation, glomerular filtration rate (GFR) estimation, anticholinergic pharmacology, and the Garden classification for femoral neck fractures.
- Runtime: 1 hour 18 minutes.
Vignette. An 82-year-old woman is admitted to inpatient rehabilitation 4 days after a left intertrochanteric hip fracture treated with a cephalomedullary nail. She has a history of hypertension, osteoporosis (T-score -3.1 at the femoral neck), and mild cognitive impairment. Her home medications include lisinopril, metoprolol, alendronate, calcium with vitamin D, alprazolam 0.5 mg three times daily for anxiety, diphenhydramine 50 mg at bedtime for sleep, and oxybutynin for urge incontinence. Her grip strength is 13 kilograms (kg), gait speed is 0.5 meters per second over 4 meters, weight has decreased 12 pounds over the past year, and she scored 21 on the Montreal Cognitive Assessment (MoCA) on admission. On hospital day 6 she becomes acutely inattentive, drowsy, and disoriented. The Confusion Assessment Method is positive.
Identify three medications on her list that are flagged by the Beers Criteria, classify her on the Fried frailty phenotype, identify the Confusion Assessment Method subtype she most likely has and which medication on her list most likely precipitated it, and state the post-operative weight-bearing status appropriate for her fixation.
(Answer at the end of this chapter)
Section 1: Aging Physiology, Sarcopenia, and Pharmacokinetic Changes
Bottom line: aging produces predictable physiologic changes that drive rehabilitation outcomes — sarcopenia (preferential Type II fiber loss with annual decline of 1 to 2 percent in muscle mass and 1.5 to 3 percent in muscle strength accelerating after age 60), peak oxygen consumption (VO2max) decline of approximately 10 percent per decade after age 25 (slowed by half with regular aerobic exercise), bone density loss accelerating dramatically after menopause, impaired thermoregulation, and pharmacokinetic shifts in which hepatic phase I metabolism falls while phase II conjugation is preserved, renal clearance drops 1 milliliter per minute per year after age 40, volume of distribution rises for lipophilic drugs, and serum albumin falls; the European Working Group on Sarcopenia in Older People (EWGSOP2) defines sarcopenia in three steps: probable (low grip strength alone, less than 27 kg males / 16 kg females), confirmed (low grip strength plus low appendicular skeletal muscle mass index by dual-energy x-ray absorptiometry), and severe (adding gait speed less than 0.8 meters per second).
Sarcopenia is the age-related progressive loss of skeletal muscle mass, strength, and function. It begins as early as the third decade with annual declines of approximately 1 to 2 percent in muscle mass and 1.5 to 3 percent in muscle strength, accelerating significantly after age 60. The pathophysiology involves motor neuron loss, hormonal decline (testosterone, growth hormone, insulin-like growth factor 1, estrogen), chronic low-grade inflammation, mitochondrial dysfunction, satellite cell depletion, decreased protein synthesis, increased myostatin expression, physical inactivity, and inadequate nutrition. The loss preferentially affects Type II fast-twitch muscle fibers (rapid forceful movements: rising from a chair, catching oneself, climbing stairs); Type I slow-twitch fibers are relatively preserved. This drives fall risk because postural perturbation recovery requires rapid forceful contraction.
The EWGSOP2 diagnostic framework is a three-step ladder. Probable sarcopenia is identified by low grip strength alone, with cutpoints of less than 27 kg in males and less than 16 kg in females by handgrip dynamometry. Confirmed sarcopenia requires low grip strength PLUS low muscle quantity, measured by appendicular skeletal muscle index on dual-energy x-ray absorptiometry (DEXA) with cutpoints of less than 7 kg per meters squared in males and less than 5.5 in females. Severe sarcopenia adds low physical performance, specifically gait speed below 0.8 meters per second over a 4-meter course.
Figure 7.2 — Aging body system schematic: full-body diagram annotating organ-system changes with rehabilitation relevance — cardiac (decreased max HR, decreased stroke volume reserve, arterial stiffening), pulmonary (decreased FEV1, decreased vital capacity, increased residual volume, blunted hypoxic and hypercapnic drive), renal (GFR decline 1 mL/min/year after 40, falsely normal serum creatinine), hepatic (decreased phase I metabolism, preserved phase II), musculoskeletal (sarcopenia Type II selective, bone loss, joint cartilage degeneration), neurologic (slowed reaction time, decreased proprioception, smaller brain volume), endocrine (decreased GH/testosterone/estrogen, insulin resistance), thermoregulatory (decreased sweat, blunted vasomotor, reduced thirst). Source needed: open-source aging physiology atlas or geriatric medicine textbook body schematic.
Figure 7.3 — Sarcopenia DEXA appendicular skeletal muscle mass: paired DEXA whole-body scan images contrasting healthy adult (normal ASMI: >7 kg/m² male, >5.5 kg/m² female) with sarcopenic elder (low ASMI below cutpoint), with appendicular muscle mass regions highlighted (arms + legs) for the EWGSOP2 confirmation step. Include grip dynamometry clinical photo for the probable-sarcopenia screening step. Source needed: open-source DEXA imaging atlas or EWGSOP2 reference figure.
Sarcopenic obesity is the coexistence of excess adiposity with low muscle mass; adipose infiltration of muscle (myosteatosis) further impairs contractile function.
Treatment centers on resistance exercise. Progressive resistance training 2 to 3 times per week at moderate to high intensity (60 to 80 percent of one-repetition maximum) improves muscle mass, strength, and physical performance even in the ninth and tenth decades. Protein intake of 1.0 to 1.2 grams per kilogram per day, distributed evenly across meals, is preferred. Leucine-rich sources (whey protein, dairy, eggs, lean meats) activate the mammalian target of rapamycin (mTOR) pathway. Vitamin D 800 to 1,000 international units (IU) daily when serum 25-hydroxyvitamin D is below 30 nanograms per milliliter.
Peak aerobic capacity (VO2max) declines approximately 10 percent per decade after age 25 in sedentary individuals; regular aerobic exercise slows this decline by up to 50 percent.
Bone density decreases with aging. Peak bone mass is achieved between ages 25 and 30. In women, post-menopausal bone loss accelerates with estrogen withdrawal at 2 to 3 percent per year in the first 5 to 10 years. Trabecular bone is affected more than cortical bone, explaining the early appearance of vertebral compression fractures.
Pharmacokinetic aging is summarized in five facts. Hepatic phase I metabolism (cytochrome P450 oxidation) decreases; phase II conjugation is preserved — a classic board distinction. Renal clearance falls 1 milliliter per minute per year after age 40, prolonging the half-life of renally cleared drugs (gabapentin, pregabalin, enoxaparin). Serum creatinine is falsely normal because reduced muscle mass produces less creatinine; always use estimated GFR for dose adjustment. Volume of distribution rises for lipophilic drugs as body fat percentage increases, prolonging benzodiazepine half-life. Albumin falls, increasing free fraction of protein-bound drugs (warfarin, phenytoin).
High Yield — Aging physiology
- Sarcopenia: Type II fiber-selective loss; 1-2% mass / 1.5-3% strength annual decline; accelerates after 60.
- EWGSOP2: probable (grip <27 kg M / <16 kg F) → confirmed (add low ASMI on DEXA: <7 M / <5.5 F kg/m²) → severe (add gait speed <0.8 m/s).
- Treatment: progressive resistance training 2-3x/week at 60-80% 1RM; protein 1.0-1.2 g/kg/day, leucine-rich.
- VO2max declines ~10%/decade after 25; exercise slows by 50%.
- Pharmacokinetic aging: phase I decreased, phase II preserved; renal clearance -1 mL/min/year after 40; serum creatinine falsely normal (low muscle); use estimated GFR; volume of distribution increased for lipophilic drugs; albumin decreased.
It is analogous to keeping your marathon runners, but losing all your sprinters. The type one fibers give you the endurance to stand or walk at a slow pace, but you completely lose the explosive power of the type two fibers.
— MEDREH-07-a podcast, ~13:07