The purpose of this study is to collect data about the efficacy of utilizing distal topical heat application for dilatation of the radial artery. Transradial arterial access is widely accepted as the standard of care for cardiac catheterization procedures due to its increased patient comfort and significantly decreased risk of major vascular complications, and has been recently utilized in increasing volume by the interventional radiology community throughout the world. Due to the small size of the radial artery, catheterization may sometimes be technically difficult. Pre-procedure dilatation can make catheterization significantly easier, and studies have demonstrated the successful ability to dilate the radial artery with the use of topical nitroglycerin and lidocaine. However, the investigators hypothesize that utilizing topical heat applied distally can create a physiologic vasodilatation similar to that created with nitroglycerin and lidocaine, but at a significantly lower cost and with less risk due to no need for application of a medication which has a systemic effect with known side effects. The purpose of this study is to test the efficacy of radial artery vasodilatation with distal topical heat application.

The study will be designed to detect a significant increase in the radial artery diameter of healthy volunteers after the application of a warm heat pack in the palmar aspect of the hand compared to a control group without heat applied to the hand. Employees and students at OHSU will be considered for enrollment as volunteers for this minimal risk study. Informed consent will be obtained from healthy volunteers prior to enrollment. After enrollment, the healthy volunteers will be randomly assigned in a 2:1 ratio to the heat group (Group 1) or the control group (Group 2), respectively. A brief medical history will be obtained from all volunteers, including age, sex, medications, prior interventions, prior surgeries, previous medical diagnoses, allergies, and any history of prior transradial procedures. For protection of confidential health information, brief medical history will be obtained in a private area. The volunteers will then be seated and the left hand placed supinated in a comfortable position on a table. A limited ultrasound of the left radial artery will be performed using grayscale ultrasound. A skin mark will be made with a marker to identify the measurement site. All volunteers will then be given a commercially available warm heat pack and asked to hold gently in their left hand. For the control group (Group 2), the warm heat pack will not be activated. For the heat group (Group 1), the warm heat back will be activated prior to placing in the volunteer's hand. Two investigators will be present. One investigator will be measuring radial artery diameter and will not be aware if the heat pack is activated. The second investigator will be aware of the volunteer's randomly assigned group and will activate the heat pack for the volunteer if they are assigned to Group 1. Over a period of 20 minutes, repeat ultrasound of the left radial artery will be performed in 5 minute intervals.

Inclusion Criteria:

• Volunteers who are 18-99 years old

Exclusion Criteria:

• Prior left transradial access for procedure

Day of radial artery measurement