The influence of methampetamine on physiologic processes and exercise

Introduction

Amphetamines are a group of drugs with mind-altering capabilities. Methamphetamine (METH) is the most potent of the amphetamine group of drugs[1]. METH falls under the classification of a central nervous stimulant (CNS). Typically, stimulants increase individuals' sensations, such as mental awareness, while also increasing one's ability to respond to the environment. Users of stimulants may also experience an increase in energy. The effects that users feel while on METH result in high addiction rates with this drug. The physiological effect of METH is achieved by increasing the quantity and release of the stimulatory neurotransmitters: dopamine, norepinephrine, and serotonin, and decreasing their synaptic breakdown[1].

A primary clinical consideration for METH is its use with other medications. Acute use of METH with other stimulants can overstimulate the sympathetic nervous system, potentially resulting in cardiac arrhythmia, seizures, cardiovascular collapse, and death[1]. Therefore, physical therapists should take special consideration when prescribing exercise to patients who present with signs suggestive of use. Characteristic presentation of METH use includes: restlessness, weight loss, heightened alertness, violent behavior, and pupillary dilation[1].

Hyperthermia

An acute response to METH use is hyperthermia[2]. Although the exact mechanism through which this is achieved is unknown, literature suggests that METH-induced hyperthermia results from heat generation as well as an inhibition in heat loss[2]. Through studying mice, researchers found that METH, especially in large doses, influences the metabolic activity of the brain due to imposing oxidative stress. Temperatures inside the brain also increase due to "enhanced release of multiple neuroactive substances, lipid peroxidation [...] and numerous changes combined as oxidative stress". Increases in the metabolic brain activation paired with internal heat production by the brain cells seem to be the driving force behind brain hyperthermia. Ingesting METH at increased temperatures or during social gatherings when an individual is more likely to be active, such as with exercise, only exacerbates this increase in core body temperature. 

Thus, combining therapeutic exercise when an individual is experiencing METH-induced hyperthermia could result in serious harm. The current practice for cooling METH-induced hyperthermia is placing the individual in a cool environment to help the body return to homeostatic balance[2].

Skeletal Effects

METH use can also have a negative effect on bone health. Through studying mice injected with METH, researchers observed that there were decreases in osteoclast activity while there were increases in osteoblast activity, resulting in increased bone formation[3]. There were also low rates of bone turnover observed, suggesting low levels of Vitamin K. Low bone turnover can result in osteoporosis. These results are important when considering excerise after long bouts of METH use. An imbalace in bone formation and the risk of osteoporosis can put the user at risk during exercise. While exercise is beneficial for bone formation, an individual using METH should avoid excessive orthopedic stress when beginning an exercise program.

Physiological Disturbances

Chronic METH use results in a range of physiologic disturbances. An adaptation with the greatest relevance to physical therapists is the presence of congestive heart failure in chronic users[4]. Impaired oxygen delivery to tissues would result in an inability to safely engage in treatment on the part of the patient. Moreover, attempting to engage in such an activtiy could result in cardiogenic shock. If the practitioner engages the patient in these activities without knowing about METH use, the outcome could be fatal. Another clinical implication is that chronic METH use can break down the blood-brain barrier (BBB) over time, and it has been shown that increased permeability in the BBB can lead to damage of myelin. Without myelin, the nervous system is unable to communicate effectively to different systems, including muscular, which could have an impact on exercise prescriptions and individual expectations.

Pulmonary Effects

METH use can have harmful effects on the pulmonary system. Research shows an association between stimulants like METH and acute pulmonary edema[5]. This can lead to acute cardiogenic pulmonary edema, which can cause other complications such as fatigue and even failure of the respiratory system to function. METH is also associated with pulmonary hemorrhaging[5]. The lungs have greater METH accumulation than the other major organs, suggesting that METH users may have an increased risk of developing lung infections or pulmonary hypertension (PAH) [6]; and METH use is strongly associated with idiopathic PAH[7].

Understanding how METH affects the pulmonary system is crucial to implementing a safe exercise plan for patients who use METH.  

Cardiovascular Effects 

Chronic METH usage affects the cardiovascular system in many ways. METH use is associated with chronic heart failure, cardiomyopathy, and structural changes in the heart, like ventricular remodeling[4]. Cardiomyopathy and ventricular remodeling makes the heart less efficient at pumping blood and at oxygenating the tissues. Patients with cardiomyopathy due to METH use are likely to become short of breath quickly. Therefore, these patients should be given a light to moderate intensity exercise plan and be able to take breaks frequently. 

Common side effects of METH usage on the cardivascular system include: tachycardia, palpitations, chest pain, chronic hypertension, myocardial infarction, aortic dissection, and sudden cardiac death[8]. Patients suspected to be METH users should be monitored during physical activity as some of these severe side effects can result in death.

Exercise increases heart rate variability (HRV) but METH usage results in decreased HRV. HRV is the interval between heartbeats representing the ability of the autonomic nervous system (ANS) to change with stimuli. So, decreased HRV represents ANS dysfunction. The researchers concluded that examination of HRV of previous METH users showed increased ANS function by decreased sympathetic outflow and improved vagal modulation[9].

Neuro Implications

In another study, the effects of both methamphetamines and exercise on the brain's prefrontal cortex were determined. The authors of this study experimented on laboratory rats and subjected them to either METH or bouts of exercise, and then studied the effects. In this study, they noted that exercise had very positive effects on prefrontal cortex activity, which includes cognition and memory, and METH had opposite effects[10]. This information, although applied to rats in this study, is clinically important because it shows how important therapy and physical activity can be for patients, and it also shows how METH can negatively affect brain activity. This can lead to physical impairments as well, so it is important to know before starting treatment with a patient that may have any METH in their system.

Exercise as Therapy

Acute exercise may help those addicted to METH. Chang, Y-K., Wang, D., & Zhou C. (2015) performed a study that looked at neuroelectric and behavioral measurements in 24 METH dependent subjects. The control group participated in an active reading session, while the experimental group used a stationary cycle for an acute, moderate-intensity exercise session. The authors found that the exercise group reported significantly lower METH "cravings during aerobic exercise and following the cessation of exercise, with the lowest craving scores observed immediately after and 50 min following the exercise session[11]." Using acute exercise to lower METH cravings is a novel idea, and the mechanisms must be explored further. The study provides an alternative to pharmacological interventions, which would be healthy and safe. We, as future therapists, could have a chance to make a big difference in the lives of METH dependent individuals.

An article by Dolezal et. al (2014) reiterated that exercise can be a proactive way to combat METH addictions and prevent relapse in recovering METH substance abusers. In this case, individuals living in a rehabilitation center for substance abuse who participated in an eight week exercise program including aerobic exercise, and muscle strength and endurance saw improvement in both categories, as well as a decrease in body composition. In this case, there was a considerable change in both physiologic functioning, as well as cognitive functioning (including combating anxiety and depression, which is common in recovering substance abusers)[12]. Knowing how exercise can positively influence a person's body as it trys to heal itself from addiction can be a major factor in our physical therapy practice and exercise prescription. 


References 

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