Acoustic sensing as a novel approach for cardiovascular monitoring at the wrist

Cardiovascular diseases are the number one cause of deaths globally. An increased cardiovascular risk can be detected by a regular monitoring of the vital signs including the heart rate, the heart rate variability (HRV) and the blood pressure. For a user to undergo continuous vital sign monitoring, wearable systems prove to be very useful as the device can be integrated into the user's lifestyle without affecting the daily activities. However, the main challenge associated with the monitoring of these cardiovascular parameters is the requirement of different sensing mechanisms at different measurement sites. There is not a single wearable device that can provide sufficient physiological information to track the vital signs from a single site on the body. This thesis proposes a novel concept of using acoustic sensing over the radial artery to extract cardiac parameters for vital sign monitoring. A wearable system consisting of a microphone is designed to allow the detection of the heart sounds together with the pulse wave, an attribute not possible with existing wrist-based sensing methods. Methods: The acoustic signals recorded from the radial artery are a continuous reflection of the instantaneous cardiac activity. These signals are studied and characterised using different algorithms to extract cardiovascular parameters. The validity of the proposed principle is firstly demonstrated using a novel algorithm to extract the heart rate from these signals. The algorithm utilises the power spectral analysis of the acoustic pulse signal to detect the S1 sounds and additionally, the K-means method to remove motion artifacts for an accurate heartbeat detection. The HRV in the short-term acoustic recordings is found by extracting the S1 events using the relative information between the short- and long-term energies of the signal. The S1 events are localised using three different characteristic points and the best representation is found by comparing the instantaneous heart rate profiles. The possibility of measuring the blood pressure using the wearable device is shown by recording the acoustic signal under the influence of external pressure applied on the arterial branch. The temporal and spectral characteristics of the acoustic signal are utilised to extract the feature signals and obtain a relationship with the systolic blood pressure (SBP) and diastolic blood pressure (DBP) respectively. Results: This thesis proposes three different algorithms to find the heart rate, the HRV and the SBP/ DBP readings from the acoustic signals recorded at the wrist. The results obtained by each algorithm are as follows: 1. The heart rate algorithm is validated on a dataset consisting of 12 subjects with a data length of 6 hours. The results demonstrate an accuracy of 98.78%, mean absolute error of 0.28 bpm, limits of agreement between -1.68 and 1.69 bpm, and a correlation coefficient of 0.998 with reference to a state-of-the-art PPG-based commercial device. A high statistical agreement between the heart rate obtained from the acoustic signal and the photoplethysmography (PPG) signal is observed. 2. The HRV algorithm is validated on the short-term acoustic signals of 5-minutes duration recorded from each of the 12 subjects. A comparison is established with the simultaneously recorded electrocardiography (ECG) and PPG signals respectively. The instantaneous heart rate for all the subjects combined together achieves an accuracy of 98.50% and 98.96% with respect to the ECG and PPG signals respectively. The results for the time-domain and frequency-domain HRV parameters also demonstrate high statistical agreement with the ECG and PPG signals respectively. 3. The algorithm proposed for the SBP/ DBP determination is validated on 104 acoustic signals recorded from 40 adult subjects. The experimental outputs when compared with the reference arm- and wrist-based monitors produce a mean error of less than 2 mmHg and a standard deviation of error around 6 mmHg. Based on these results, this thesis shows the potential of this new sensing modality to be used as an alternative, or to complement existing methods, for the continuous monitoring of heart rate and HRV, and spot measurement of the blood pressure at the wrist.Open Acces

Self-Indulgence or Loss of Self-Control? Or, is it a Bit of Both? Investigating Cross-cultural Aspects of Impulse Buying Behavior

Impulse buying is considered an important and widespread phenomenon by consumer researchers as well as marketing practitioners in the US and other western countries and it has been considered largely universal in nature (Beatty and Ferrell 1998; Hausman 2000; Rook and Fisher 1995). However, recent research has highlighted the need to explore the cultural context of consumer behavior to help the marketers understand and capitalize on cross-cultural differences in an increasingly globalized marketplace (Maheswaran and Shavitt 2000). In this context, some researchers have begun to investigate impulse buying behavior in other countries besides US such as Australia, Hong Kong, Singapore, Malaysia and Vietnam (Kacen and Lee 2002; Nguyen et al. 2003). On the other hand, there is also a growing demand to establish measurement equivalence for scales developed with the US consumers before using these in countries outside the US (Sharma and Weathers 2003; Steenkamp and Baumgartner 1998). Unfortunately, most cross-cultural studies into impulse buying used scales did not adhere to the suggested methods to demonstrate measurement equivalence, despite using scales developed in the US among their non-US subjects. Hence, there is still no conclusive evidence to support the assumption that impulse buying has the same meaning and implications across cultures

Impulse buying and variety seeking: Two faces of the same coin? Or, maybe not!

Impulse buying (IB) and variety seeking (VS) are both classified as spontaneous hedonic purchase behaviors influenced by feelings rather than logical thinking (Baumgartner 2002). However, there is little empirical research into their similarities and differences. We address this gap by investigating the association of both these behaviors with relevant consumer traits (consumer impulsiveness, optimum stimulation level and self-monitoring) and situational factors (involvement, product type, time availability and mood)

Looking Beyond First-Person Effects (FPE) in the Influence of Scarcity Appeals in Advertising: A Replication and Extension of Eisend (2008)

In this paper, we replicate and extend Eisend’s (2008) pioneering work on first-person (FPE) effects in the context of scarcity appeals in advertising, using ‘influence of presumed influence’, a broader and less restrictive theoretical perspective compared to FPE to develop a revised conceptual model. Specifically, we hypothesize that it is the perceived influence on self and others, rather than the difference between them as hypothesized by Eisend (2008) that mediates the impact of value perception on purchase intention. Using a student sample similar to Eisend (2008) albeit with a different product category and advertising stimulus, we found that value perception has a direct positive effect on the perceived influence on others that affects the perceived influence on self, which in turn influences purchase intention. Besides offering an alternate model for future researchers to explore the role of scarcity appeals in advertising, our findings may also help advertisers focus on the perceived influence on others and use it to influence consumers’ own value perceptions and purchase intentions

Scarcity Appeal in Advertising: Exploring the Moderating Roles of Need for Uniqueness and Message Framing

In this article we examine differences in the impact of message framing and scarcity appeal types in advertisements on consumers with varying levels of need for uniqueness (NFU). Results from two experimental studies support a two-way NFU × scarcity interaction, wherein participants with lower levels of NFU show a greater impact of demand (versus supply) scarcity appeal on their attitudes and purchase intentions; whereas participants with higher levels of NFU show a greater impact of supply (versus demand) appeal. In addition, we found support for a three-way interaction, which shows that, under both gain and loss frames, participants with lower levels of NFU prefer demand over supply appeal; whereas under the loss frame, participants with higher levels of NFU prefer supply over demand appeal. We discuss the conceptual contribution and managerial implications of these findings

Consumer ethnocentrism vs. intercultural competence as moderators in intercultural service encounters

Purpose – This paper aims to explore the moderating effects of consumer ethnocentrism and intercultural competence on the impact of service outcome and perceived cultural distance, respectively, on interaction comfort and perceived service quality in intercultural service encounters. Design/methodology/approach – A 2 X 2 between-subjects experimental design with university students was used, using service encounter scenarios to manipulate service outcome (failure or success) and photos of service employees to manipulate perceived cultural distance (low vs high). Findings – As hypothesized, the impact of service outcome on interaction comfort and perceived service quality is moderated negatively by consumer ethnocentrism, whereas the impact of perceived cultural distance is moderated positively by intercultural competence. Research limitations/implications – An experimental design using imaginary service scenarios was used in a single service context (i.e. restaurant) with university students as participants, which may restrict the generalizability of our findings. Practical implications – Managers in service firms with multicultural customers should try to recruit service employees with high intercultural competence and low consumer ethnocentrism. They should also develop employee training programs that help minimize the adverse impact of these variables on interaction comfort and service quality in intercultural service encounters. Originality/value – This paper extends prior research by exploring the moderating effects of consumer ethnocentrism and intercultural competence on the direct and indirect effects of service outcome and perceived cultural distance on interaction comfort, service quality and satisfaction