Power Safety Standards for Home Medical Devices

Internal medical AC/DC power supplies and external medical AC/DC power supplies have 60601-1 certification for 2 x MOPP (means of patient protection). [Photo courtesy of CUI]

Patients using blood pressure monitors and CPAP devices in non-clinical settings are protected by IEC 60601-1-11.

Ron Stull, UI

Home medical devices can be an excellent first line of defense when it comes to health and medical issues, and there is an increased need for home care for patients discharged from hospitals and other healthcare facilities.

Medical technologies used in non-clinical settings vary in complexity, ranging from simple materials to deliver first aid to sophisticated devices to deliver advanced treatments.

Complex home electrical medical devices must comply with stringent IEC 60601-1 safety standards for medical patient protection. They must also meet additional requirements related to hazards in and around the home, such as untrained equipment users and the uncontrolled home environment.

Blood pressure measurements

Blood pressure is an essential vital sign guiding acute and long-term clinical decision-making. Generally, blood pressure measurement collects systolic pressure and diastolic pressure.

Systolic pressure is the peak blood pressure during systole, when the heart muscle pumps blood from the chambers into the arteries. Diastolic pressure is the minimum blood pressure during diastole, when the heart muscle relaxes and fills the cavities with blood.

Mean arterial pressure (MAP) is calculated from systolic pressure (SP), diastolic pressure (DP), and pulse pressure (PP) using the following equations: MAP = DP + 1/3 ( SP – DP) or MAP = DP + 1/3 (PP).

A pressure sensor measures the patient’s systolic and diastolic pressures as the cuff deflates. For example, an AC-powered, wheelchair-accessible blood pressure meter has a cuff and an elbow sensor inside the device that automatically adjusts to ensure the patient is in the right position for highly accurate results every time.

The blood pressure measurement system requires an AC/DC power supply that meets IEC 60601-1 electrical safety requirements and the requirements for home use set forth in the collateral standard IEC 60601-1-11. A series of internal AC/DC power supplies or an external series of wall outlet adapters meet home medical power needs and security concerns.

Compliance with IEC 60601-1-11 requires power supplies to be classified with IEC protection class II due to the assumption that the electrical environment has poor or no protective earth conductor. Class II power supplies provide the appropriate level of protection without depending on protective grounding by applying double or reinforced insulation.

CPAP systems

The gold standard for obstructive sleep apnea (OSA) devices is continuous positive airway pressure (CPAP). The AC-powered CPAP machine provides constant air support for nighttime breathing difficulties such as apneas, hypopneas and snoring. The machine connects directly to the patient in medical, clinical, hospital or home environments.

Automatic CPAP features are essential due to intended use by untrained operators. The device reacts to the patient’s breathing breath by breath and the reading of these reactions by the machine eliminates the need to adjust settings by home healthcare operators. Additionally, the CPAP machine offers climate control, which automatically adjusts the humidity and temperature of the delivered air. Humidity and temperature measurements provide optimal comfort and protect the patient from condensation in the mask and tubing.

The home environment may contain a variety of devices that emit electromagnetic noise that may interfere with the operation of medical equipment and sensors. Home medical devices must meet stricter requirements than traditional medical equipment to limit potential interference from their own emissions. For example, traditional medical equipment must meet CISPR 11 Class A emissions, while home medical equipment must meet the more stringent Class B limits.

CPAP machines can use cellular, Bluetooth Low Energy, or Wi-Fi connections to upload data to a cloud service, but reliable communication requires minimal interference. The wireless connectivity of CPAP devices also enables telehealth/telemedicine to help address common CPAP performance issues such as inconvenience and difficulty in use. The CPAP device requires an electrical connection that complies with the IEC 60601-1-11 medical safety standard. Wall-powered CPAP devices use an isolated AC/DC power supply that complies with IEC 60601-1-11.

Some portable CPAP devices run on battery power while on the go. The CPAP system and other portable medical devices must meet more severe shock and vibration tests, as well as additional mechanical stress tests. With battery power, the AC/DC battery charger configuration still requires a connection that complies with the IEC 60601-1-11 medical safety standard.

The IEC 60601-1 isolated AC/DC power supply should allow for +10/-15% mains power variation to account for less predictable residential power infrastructure. This means an input range of 85 to 264 Vac for universal operation.

The motor and sensor systems are located below the battery charger and non-isolated DC/DC power supply structure. The motor system includes a fan assembly that pushes air through the tube of the nasal mask. The sensor system uses multiple sensors to measure the humidity, temperature and flow of the nasal mask.

Electrical topology of a CPAP device, containing the power supply, sensors, ventilator motor, and patient interface [Illustration by CUI]

Conclusion

Home electronic medical devices monitor and assess an individual’s health and provide data for early diagnosis and future treatment advice. This article has used examples of electrical blood pressure and CPAP systems with IEC 60601-1 electrical power backbone and sensing technologies to demonstrate home diagnostic electrical equipment. Due to differences between home and hospital, home medical devices must meet IEC 60601-1-11 safety requirements.

Ron Stull, Energy Product Marketing Engineer at CUI [Photo courtesy of CUI]

Ron Stull, Power Product Marketing Engineer at CUI, is an experienced engineer with knowledge and experience in analog power, digital power, and AC/DC and DC/DC power conversion. He joined CUI in 2009 and has held key positions in various facets of engineering (including application support), test and validation, and design.

The opinions expressed in this article are those of the author alone and do not necessarily reflect those of MedicalDesignandOutsourcing.com or its employees.

Alan A. Seibert