Heart Rate Variability is Altered in College‐Aged Chronic Cannabis Users versus Non‐Users

Abstract

Cannabis is an increasingly popular recreational drug among college students. Prior investigations have shown that acute cannabis use alters heart rate variability via increased sympathetic activation. However, the effects of chronic cannabis use on heart rate variability (HRV) have not been reported. PURPOSE We tested the hypothesis that HRV would be lower in chronic cannabis users (THC) compared to non-users (CON). METHODS Eleven cannabis users (age: 21±2 y, 2 females) and six controls (age: 20±2 y; 4 females) completed one study visit. Participants in the THC group self-reported using cannabis at least once per week for the past year or more. Participants in the CON reported to not use for 6 months prior to enrollment. Participants were instructed to abstain from alcohol for 24 h and cannabis for 72 h prior to the study visit. After 10 minutes of supine rest, heart rate (5-lead electrocardiogram) was continuously recorded at 1 kHz for 5 minutes of supine rest while participants breathed spontaneously. HRV was assessed using linear analysis via Fast Fourier transformation and non-linear analysis via Poincare plots. The root mean square of successive differences (RMSSD), percent of R-R intervals that differ by more than 50 ms (pRR50), and the standard deviation of R-R intervals (SDRR) were calculated to assess HRV in the time-domain. Fast Fourier transformation was used to assess HRV in the frequency domain (low-frequency (LF) and high-frequency (HF) power). Non-linear HRV analysis was performed using Poincare plots to calculate standard deviation 1 (SD1) and 2 (SD2). We used one-tailed unpaired t-tests to determine if the main outcome variables were different between groups. Values are reported as mean ± SD. RESULTS RRI was lower in THC (THC: 917±109 vs. CON: 1018±141 ms; P=0.06). RMSSD was lower in THC (THC: 57±21 vs. CON: 74±24 ms; P=0.07). There was no difference between groups for pRR50 (THC: 36±20 vs. CON: 47±21 %; P=0.12) or SDRR (THC: 68±16 vs. CON: 78±24 ms; P=0.15). LF power was not different between groups (THC: 1105±850 vs. CON: 1321±852 ms2; P=0.31), but HF power was lower in THC (THC: 1353±925 vs. CON: 2256±1195 ms2; P=0.05). SD1 was lower in THC (THC: 40±15 vs. CON: 53±17 ms; P=0.07). SD2 was not different between groups (THC: 86±19 vs. CON: 96±33 ms; P=0.23). CONCLUSION These preliminary data indicate that college-aged adults who regularly use cannabis have lower heart rate variability than their non-cannabis user counterparts. Based on linear and non-linear analyses, it appears that cannabis users have altered cardiac vagal activity at rest. However, more research is warranted to determine if cannabis use alters autonomic function and reactivity.